In the past, I've had nausea for months that was due to anxiety... It was possibly the most horrible time I went through (mostly because nausea really sucks, and it being constant for months sucks even more) But it only emerged when I stopped having any specific triggers or symptoms mostly, which was odd. It was also very aggravated whenever I was under more stress than usual. It sorta went away by itself after maybe 3 months. I also get nausea whenever I have a major anxiety attack now, and sometimes just with depression.