I know exactly what you're talking about... I've been there so many times. I have an inner ear disorder which is undiagnosed, and it's been that way for almost 4 months now. I've spent way too many hours trying to figure out what it is on my own after 2 doctors told me it would go away on it's own.
What I've done to avoid some of the anxiety is limit my time searching, because it's very easy to caught up in it for hours. I also try to end every session of my research on a positive note, which this message board has helped me with. I found a lot of people who have symptoms similar to mine and they're getting better all the time.
I basically treat my researching like caffine (when I used to drink it); limit my intake, don't do it if I'm too strung out already and never before bed!