I've worked at a million jobs, and I know there's a fine line between "I've got to suck it up" and "I'm going to go quit RIGHT NOW, for the sake of my mental health." I think, based on my experience, that if you don't have children or other financial responsabilities that couldn't be met by, say, a part time job (at least while you look for another full time one), and you're really unhappy, then you should quit.

The problem is defining "really unhappy". Maybe your job makes you want to cry on a regular basis (been there) or your dignity gets trampled on (been there too... NEVER work in outside sales!), or maybe you have nightmares about work and call your mom exclusively to complain about work and complain to friends about work during, say, birthday parties, and suddenly realize that you're obsessed with work because you hate it so much that you can't get it out of your head. In any of the above cases, I'd say you need to quit. If you simply hate having responsabilities, and getting up early, and not having as much free time as you'd like (no one does, if they have full time jobs), then you'll either have to get used to it, or get a smaller job while you get used to the real world, and risk losing a great job.

Also keep in mind that "great jobs" aren't always great jobs for you. And there's always going to be another chance. And stop feeling guilty about being unhappy, or else you'll wind up settling for things in life that you shouldn't ever had put up with.

Hope this helps,

Liz