One tool I use to help prevent meltdowns is a ten-point "stress scale". If I'm getting close to a 7 on the ten-scale, I know it's time to start looking for ways to reduce the stress level ASAP. If I'm at a stage 2, I know I can afford to do things that might raise my stress level. It helps me not to miscalculate how much I can take, rather than being either overly avoidant or just rushing in without thinking about whether or not I'm up for it, with the inevitable, embarrassing, result. Using strategies like this has helped me reduce the frequency of all-out meltdowns from multiple times a week to no more than a couple times a month, and even those mostly in private.
The use of a ten-point stress scale is actually a relatively common tool, not just for autistics but for people with chronic illness (to gauge what they're capable of doing that day) and people with mental illnesses (to monitor symptoms and increase self-awareness). I actually got the idea to post about this from a book I linked to a few weeks back (Congratualtions, Your Child Is Strange), along with the realization that not everybody knows about this kind of a method.
I should caution anyone who begins using a stress/overload ten-scale to remember that the purpose of using one is not to focus on one's discomfort and, by focusing on it, make it worse; it's to have a way of knowing when to take action and deal with the problem. Thus, if you use a ten-point scale, make sure to have solutions for the problems you will be facing on the higher levels--solutions that are flexible enough to implement in most environments, and simple enough to remember and carry out when you are under that level of stress.
Needless to say, my ten-scale does not apply to all autistics; it applies only to me, personally, because everyone's sensory, communication, and cognitive traits are different--if you want one for yourself, you will have to write your own. Some people might lose speech at stage 5, or be able to communicate coherently all the way up to stage 9. Others might not experience muscle tension as a sign of overload. And many will have different baselines. It will vary during your lifetime; most people become much better at preventing meltdowns as they grow older and learn how. But these are how it happens to me.
Description: Completely Relaxed
Physical: Steady heart rate; no muscle tension
Cognitive: Able to access all skills, but actually doing so will increase stress level.
Social: Able to efficiently communicate, but actually doing so will increase stress level.
Sensory: Quiet room, no sensory stressors. New stressors will not increase overload.
Frequency: Almost never. Sometimes for a few minutes after just having woken up.
Description: Minor Effort
Physical: Steady heart rate; muscle tension associated with physical activity or awkward posture
Cognitive: Probably engaged in a special interest; able to access all skills; not engaged in activity which is difficult or frustrating
Social: Probably alone; able to access all communication skills, but doing so would increase stress level
Sensory: Quiet room, sensory stressors limited to very minor problems (air conditioner humming, tight socks, smell of food). New stressors will not increase overload.
Frequency: Sometimes, when engaged in special interests.
Description: Normal Effort; NT baseline
Physical: Steady heart rate; muscle tension associated with physical activity, awkward posture, occasional minor anxiety
Cognitive: May be experiencing transient frustration (<1 minute), but access to all cognitive skills is available
Social: May be having a one-on-one conversation with a familiar person about a favorite subject.
Sensory: Multiple minor sensory annoyances, but none are interfering with thinking.
Frequency: Some periods of this on most “good days”.
Description: High Effort; low-level, long-term stress
Physical: Constant awkward posture, constant muscle tension. Constant minor anxiety.
Cognitive: Access to all cognitive skills, but frustration level is lowered. At this point, exposure to transitions, frustration, or high sensory load will escalate stress level.
Social: May be caused by having a conversation with multiple people in a quiet room. All communication skills accessible.
Sensory: One or more moderate sensory annoyances present.
Frequency: Some periods of this on most “good days”.
Description: Moderate Stress; NT on a "bad day"; autistic baseline
Physical: Constant minor anxiety; constant muscle tension. Physical awkwardness increases.
Cognitive: Access to all cognitive skills, but endurance and frustration tolerance are drastically lowered. Test performance starts to suffer.
Social: Communication becomes less sophisticated; more scripts are used. Still able to communicate when desired, but tend to withdraw. No longer able to multitask tone-of-voice and word meaning.
Sensory: Sensory input becomes more difficult to process; minor/moderate sensory annoyances have more impact on stress.
Frequency: Represents the best parts of “bad days” and the worst parts of “good days”.
*At this point, stress levels start to "snowball" where each new stressor means less tolerance for the ones already present.
Description: Mild Overload
Physical: Constant muscle tension. Probably stimming visibly in an effort to calm down because I have abandoned any efforts to look typical and not annoy people. Constant moderate anxiety. Heart rate increases. Motor planning is inadequate and driving a car in heavy traffic is a bad idea.
Cognitive: High-level cognitive skills have been dropped; probably unable to multitask or use skills that are very demanding on working memory. Attention span decreases. Careless errors become common.
Social: Communication is mostly by rote, but able to communicate when desired. Definitely withdrawing by this point. Becomes impossible to process conversation in a crowded room.
Sensory: Minor sensory annoyances feel like moderate ones; moderate ones become unbearable.
Frequency: Happens multiple times a week for an hour or more before escalating or subsiding, after intense cognitive effort or while physically tired. Can be de-escalated by quiet time alone.
Description: Moderate Overload
Physical: Constant muscle tension that feels more like fever or pain than tension. Constant moderate anxiety and probably embarrassment. Motor planning is inadequate, and driving a car at all is a bad idea.
Cognitive: High-level cognitive skills are unavailable; multitasking is impossible; directing attention is impossible. "Zoning out" due to overload is common.
Social: Able to communicate simple ideas and formulaic conversations without delays; more complex ideas can be communicated but take some thought to get out. Communication may not carry the correct meaning.
Sensory: Any sensory annoyance will escalate stress level.
Frequency: Happens a few times a week. At this point I will start to put meltdown-prevention strategies into practice.
Description: Meltdown Threshold; NT during a major disaster or after a breakup or death of a loved one; autistic during a "bad day"
Physical: Holding self upright is beginning to feel like too much effort. Anxiety about impending meltdown; desperation to "escape". Riding a bike has a high chance of resulting in an accident.
Cognitive: Unable to plan, think logically, or problem-solve. Unable to choose between two or more alternatives. Still able to follow simple pre-arranged plans. All high-level skills unavailable; most mid-level skills unavailable. May be crying, though usually trying to inhibit it.
Social: Any communication takes thought, and probably must be mentally written before it can be spoken. Any available communication will be simple. Still capable of hearing and understanding, but not able to process words well.
Sensory: Any sensory annoyance will escalate to complete meltdown.
Frequency: Once or twice a week. Meltdown-prevention strategies take number-one priority.
Physical: May be unable to figure out how to move. May be very tense and curled into a ball. Likely to hit anyone who attempts to touch. Heart rate sky-high; fight-or-flight system fully activated.
Cognitive: Unable to think rationally. Likely to be crying uncontrollably.
Social: Has mostly forgotten other people exist. Cannot interpret speech. Any communication will be either meaningless or repetitive on one or more phrases.
Sensory: Sensory processing is either absent or ultra-sensitive. Jerking away, flinching, or lashing out at the source of physical contact or noise is common.
Frequency: Two to three times a month. Happens mostly when trapped in situations where withdrawing is impossible.
*Most NTs will never experience this, but it is not impossible. NTs have meltdowns on occasion, too, especially when really horrible things happen to them.
Description: Extreme Meltdown/Shutdown
Physical: Repetitive self-injury out of desperation; possible complete immobility in a catatonia-like state. Unlikely to be able to stand; may be aimlessly kicking and hitting. Unable to respond to pain or danger.
Cognitive: completely unable to think rationally. Screaming and crying are inevitable. Lacks cognitive ability to purposefully destroy objects or aim for any target if lashing out. May not remember parts of the meltdown later.
Social: Has forgotten other people exist. Speech is absent; ability to interpret speech is absent. Other people are treated exclusively as unwanted sources of sensory input.
Sensory: Sensory processing is completely disorganized; unable to recognize surroundings.
Frequency: Once or twice a year. Usually happens if someone tries to stop a meltdown while I’m already in stage 9. If it happens in public, will usually result in police being called.
Stages 1-4: No Response Needed
Stages 5-6: New stressors should be avoided. Unnecessary activities involving cognitive/sensory stress are dropped.
Stages 7-8: Attempt to seek a private, quiet place to prevent escalation. If stage 8 and at school, find disability services office in case of meltdown. Otherwise, head home as soon as possible. If heading home is impossible, find a public restroom or other hidden spot.
Stages 9-10: Unable to use coping strategies. If capable of moving away from uncomfortable sensory input, do so.