2 1/2 year old started to twitch at night after returning from vacation where he was traumatized by a stressful situation. could stress be the culprit?

Twitching: Twitching can be due to a variety of reasons including electrolytes or abnormality in central nervous system . Evaluation by a physician is necessary to rule out any cause other than stress.

Hard to say: Your description is too vague to comment. Night twitching could be benign sleep myoclonus or signs of a serious problem. If this is new and worrisome you need to schedule a visit for a real evaluation.