One of the things I learned running my first startup was that I really don't enjoy running a business. The mountains of admin work, the never-ending decision making, the constant anxiety of whether or not I made the right call, the pressure to never actually switch off and just work work work, all of the pointless 'networking' with people who're pretending to be interested ... it all adds up to a pretty horrible experience. The high points (raising a successful round, first revenue, first hires, etc) kind of make it worthwhile, and obviously an exit is nice (not that I'd know... I've never got to that point), but I don't think I'd do it again unless I have an amazing idea that I have to build.
Anyone who tells you being a C-level person in a startup is fun and glamorous isn't running a real startup.