Why do i not want to eat when stressed or anxious?

Stress leads to acid: In majority of humans stress causes brain to release stress hormones, which indirectly cause excessive acid production in stomach. Little increase in stomach acid causes hunger but a lot of it causes decrease in appetite and at times heart burn.

Fight or flight: Some people eat more when stressed; others eat less. It depends on your system's neural balance. If you're more towards the "flight or flight" end of things, sympathetic nervous system will be in charge -- suppressing GI function. The parasympathetic system is more in charge of eating and digestion. When you relax (and these systems are more in balance), your GI function normalizes again.