Regression is a problematic occurrence that happens with some individuals on the autism-spectrum after there has been significant gains being made in cognitive development, social interaction, etc. Sometimes the regression pattern is sudden. Here are some clues:
Dietary Infractions - this is high on the list. Sometimes a hidden ingredient, or a change in ingredients that you are not aware, i.e. from a Gluten-free, Casein-free food. Also, getting sabotaged with the diet - not necessarily intentional - from friends, family members, at school, a new therapist, your child getting into another child's lunch, etc.
Supplement Changes - sometimes a new supplement, or a new ingredient in a supplement can cause regression. An example would be a change in the amount of particular vitamin - such as B6, or a new flavor for Cod Liver Oil. Also, increasing the amounts of supplement(s) could contribute to regression.
Other Food Exposure - such as dyes, preservatives. Or new natural foods that are high in phenols - grapes, plums, bananas, etc.
Yeast Overgrowth - this is very common, and can come on quickly. Sometimes you will not know what caused it. I have seen kids get yeast issues following a cold, flu or even allergies from the environment. In Southern California there are Santa Ana winds that blow warm air in from the deserts about 4 to 6 times per year. This usually brings a lot of allergens with it. Other regions have their own unique environmental changes. Increase in allergy can cause a shift in the immune system with increased inflammation. A trial of anti-fungal medication like Diflucan or Nystatin, or natural remedies like Grapefruit Seed Extract can help. If it is a yeast issue, the behavior will shift for the better in 5 to 7 days. Also, if allergy is suspected taking an anti-histamine could help.
Time Cycle Changes - regression patterns can occur with time changes - summer to fall, fall to winter, winter to spring, etc. This commonly occurs with sudden changes in dark and light cycles - particularly in areas when the clocks move backwards or forwards twice yearly.
Stress - change at school or therapy. A new challenging task, new teacher, new kid(s) is class. Anything that is upsetting the routine that a child is use to. The same pattern can occur at home with new or sudden changes.
Recent illness or coming down with a cold/flu/Allergies - see above explanation under Yeast Overgrowth.
Constipation or sluggish bowels - many times a change in bowel function - usually with a child going through a period of sluggish bowels - can create a situation of increased bowel toxins. These toxins get absorbed and create imbalances in the body and brain. Giving some additional magnesium to bowel tolerance - as citrate - can help to improve bowel function. Bowel tolerance means the 'point at which loose stools occur' is the time to cut back on the dose of magnesium. Magnesium can also help with hyperactivity. If needed, a laxative or child's enema can help clear the bowel of stored up stool.
Growth Spurt - regression in kids can sometimes occur with a growth spurt. Many times when children go through growth spurts they have an increased appetite or sleep more soundly at night.