I've been a startup founder of one form or another for pretty much my whole adult life.
I have stress or anxiety when things are up in the air (positive or negative), but happiness or unhappiness has a lot more to do with factors other than the startup. Mostly because I believe in expected value and statistics -- there's a lot of randomness in everything, and you can do things which influence probabilities substantially, but if you've done that and there's an 80% chance of a good outcome, the actual result doesn't mean you're doing well or poorly as much as whether the odds were 80% or 30%.
My goal is to try to use skill, connections, effort, etc. to raise the expected returns as much as possible, then just take a lot of shots to get the right returns. Worry before things are resolved, not after.