Have some chocolate. Or a cookie. Or a shot of vodka.
Breathe some more.
Try not to stare at your computer like this:
(Blink at least once in a while.)
There will be times when you hear back before other people and times where you NEVER hear back from agents who supposedly usually reply or seem to have already replied to everyone except you. Sad, but true.
The trick is to let it bother you as little as humanly possible and keep moving forward. Send out a few more queries. Research some more agents. Work on another project. Polish your synopsis. Step away from the computer. There's no way to get around the compulsive need to refresh your inbox, so just accept that it's gonna happen and that you're not alone. There are countless people who sympathize and also wish you well. Stay busy and focus on the things that keep you sane. And, most importantly, during those times when insanity/hysteria/paranoia win out, ride them out, calm down, and remind yourself that it's all just part of the process and is perfectly normal. Not fun. Not glamorous. But normal.