No more so than the theistic population. Most are well adjusted, reasonably happy people struggling to get through life like anyone else. Many are involved with community, charity and society. Atheists are not pessimists.

Atheists prefer not to comfort themselves with fantasies, but rather establish their ego and outlook on life through real things - careers, friends, family, hobbies, and life in general.

"Deconverting" can be an unnerving experience, though, where depression and bewilderment can follow. This is typically because, as a theist, one has an emotional structure built around religion. Once that infrastructure is removed, it can take awhile before one can build a new, reality-based, emotional infrastructure.

Many atheists express that they are generally happier without religion. Depending on the type of god one worships, anything good or bad that happens to a person is attributed to that god. When bad things happen to an atheist, we analyze it and see what we could do better, but otherwise shrug it off as "shit happens" - there's no invisible force behind the scenes trying to punish us. That is a lot less nerve wracking than a religious person trying to figure out what he/she did to anger the god, second-guessing the motives of an entity that can't even be demonstrated to exist.

Atheists have described letting go of these beliefs as having a weight lifted off their shoulders - letting go of the guilt for merely being human.

Losing faith can seem like a loss, but the key point is that one really hasn't lost anything but a delusion.

The problem is not losing the faith. The problem is that one was deceived into thinking the faith was a good thing, in the first place. That is what most new atheists eventually realize and embrace. Many Christian teachings spend a lot of time convincing their followers that they are worthless, and the only way they have any value is through Jesus, for instance. This is not a positive teaching. Losing this particular teaching would be a step in the right direction towards happiness.