Times I've been withdrawn was:
-Unwillingness, which may not happen anytime soon because I still want to learn and I'm bored.
Any form of willingness will do, and curiosity is a good start. Though there may be other factors to obstruct this.
-Fear and worry induced anxiety from all the failures accumulated.. That I already overcame long time ago and failed to come back at me.
This is very tricky to overcome. Even harder in case of ASD. It requires some form unlearning/relearning, gradual realization and acceptance. 'Coping' through persistence and meds is a short term short cut.
-Perhaps, strong emotions. Too strong to respond and respond to... Which isn't common and does not stick for too long in my case.
This requires enough maturity to master. And enough introspection to understand.
-Being overwhelmed. Also rare in my case.
It's about how the mind and body takes the input, sensitivity or not. Depending on your needs if it requires moderation or something specific.
-Being exhausted. In any ways - physically, mentally, emotionally.. Also rare. Too rare in my case. I happened to have more stamina and rarely get sick or weak.
It's about moderation, knowing your own limits, and when and how to take a break. And more factors how to conserve and spend less energy, or extend energy.
-Mentally too preoccupied or too focused on something else. This is the closest reason why I might withdrawn.
To overcome this, means to tolerate change or through adaptation. And able to switch gears, which is very jarring when done wrong.
-Certain fulfillments to expand 'territory' or comfort zones. Let's just say more than 6 years ago, I only have my room, my house and my family. Then the school, my house, the faculty staff, and my family. And eventually ended up pacing across the whole village, and then the whole city and with strangers.
This takes time and experience. LOTS of it. But this part helps in the long run.
-Sometimes... It's nothing.
Even so, people presence still bothers me somehow that is if I simply want to withdraw without the reasons above. Especially when I'm not really in a mood to entertain anyone. But there's no anxiety or what thought. Annoyance more likely.
More like being invaded by the physical presence itself (not the people themselves or their actions), though I can take it. At worst, I just stop what I was doing and move somewhere else.