Sometimes full time work, and the environment and requirements, are just really stressful for certain people (like me). One hope would be that with time, the stress of the new job would come down, you'll get more adjusted to the new routine and requirements, so that the stress level comes down, and you feel more back to normal. Alternatively, are there any triggers you can notice? Background noise? the lights? For me I hate fluorescent lights, I hate lack of privacy, and even the constant low hum of computers gets to me. Headphones, a longer lunch break, anything like that that could help you?