My son is also 24 was in a self contained class throughout his school years. Smart made honors. My son too gets very upset and angry w/ his sister who has OCD and BPD. There are times when our conversations turn into an argument. I will tell him something and then it turns into an argument. The best thing that helped my son was the fact that he decided to go to college. He now has a routine, he's eating better, and he's doing a lot of walking. Does your son have a regular routine? If not then maybe that's what he needs. I noticed that now he's easier to talk to and doesn't argue as much.

A sudden or notable change of behavior in an autistic adult is often a warning sign of physical pain, environmental stress, or Autistic Regression in Adults rather than a permanent change in their personality.

Common Causes of Behavioral Changes

• Medical or Physical Issues: Undiagnosed pain, dental problems, headaches, gastrointestinal discomfort, or infections can cause an adult to act out, withdraw, or show increased irritability because they cannot easily describe what hurts.
• Autistic Burnout and Regression: Long-term masking, chronic sensory overload, or exhaustion from daily demands can lead to a drop in executive function, loss of communication skills, or withdrawal.
• Major Life Transitions: Moving, changing jobs, losing a routine, or shifts in family status (such as a breakup, marriage, or death of a loved one) can trigger intense anxiety.
• Co-occurring Conditions: The onset or worsening of anxiety, depression, or sleep disorders can heavily alter behavior and energy levels.
• Sensory or Environmental Overload: Unchecked changes in lighting, noise levels, schedule disruptions, or loss of personal space can cause emotional dysregulation.

How to Respond and What to Check

• Rule out medical causes first: Schedule a visit with a doctor or dentist to check for hidden physical pain, illness, or side effects from medication before assuming the change is purely behavioral.
• Inspect the environment: Look for recent changes in noise, lighting, daily routines, or social demands that might be causing hidden stress.
• Reduce demands and support rest: Allow extra time for recovery, limit unnecessary social or work pressures, and re-establish predictable routines.
• Consult a professional: Work with a therapist, neurologist, or occupational therapist experienced in adult autism to evaluate triggers and adjust support strategies.

https://neuronav.org/self-determination-blog/un...

Understanding Autistic Regression in Adults

https://neuronav.org/self-determination-blog/understanding-autistic-regression-adults