Sure it's all in my head, but the thermometer says it's in my bloodstream too!
In fact, having a partner is the single best thing that has happened to my stomach and my insomnia. She reduces my stress levels and alleviates the symptoms very noticeably just by being by my side. Sorry if it sounds corny, but for me this is an observable reality.
The problem with all this is that, of course, stress is often something outside our control. Knowing what I know I try to keep it at bay as much as possible and take things easier than when I thought it was a food problem, but if there's lots of work and deadlines it's not like you can just wave stress away like you can avoid a given food...
Most of the comments here, people seem only capable of introjecting stuff as if the sole reason for stuff has gotta be personal issues(not saying this in a derrogatory manner) or a square diagnosis, this is absurd to me. Maybe it's cause I already came to the conclusion that I'm an ok mostly healthy animal plus gave up trying to fit the artificial into the natural(i.e.: I think our society is rotten. Also, how convenient it is that all problems must be seen as purely individual, huh?). History, classical thought -> good for the brain and body, maybe.
During that period I was ok, probably surviving on fight and flight, but since I've had episodes as you describe, although one case with a super high temperature that left me unable to work for 3 days.