I haven't managed to sell a business, yet, but when I decided to give up and get a job last year, I got a less intense (and probably less long lasting, though it's still going on to some extent now) version of this. The lack of stress after 7 years of never knowing if there was going to be enough money next month was palpable.
I don't think it's necessarily a money thing, because I experienced the same effect when I folded up my startup and got a job. And I still had enough cash in the bank to do one, maybe two more startups, and was never in any danger of running out of money.
I think it comes from the sudden lack of responsibility. When you're in a startup, everything you do matters: if you succeed, it's because you rocked, and if you fail, it's because you screwed up. This makes you feel incredibly alive, but it's also incredibly stressful. When you go back to collecting a paycheck and have to grotesquely screw up to get fired, all that stress just evaporates, and it's like coming down off a massive high.
I still wanna try it again, and hopefully end up with a success instead of a failure next time. But I felt like I'd reached the end of my endurance when I gave up: I'd given it my 110% and it still wasn't enough given my current experience level. I wouldn't trade the experience for anything though.
I agree that it's not just the money; it's just that the money was what was on my mind all the time, because I was losing/borrowing money rather regularly for 2/3 of that seven years. :) I also plan to try it again, fairly soon, even. It's one reason why I'm working contracts now instead of full-time.
