Lots of people make 'big" changes when they hit this point in their lives, thinking that life will be better on the other side of whatever change they've made happen. Big changes that I am talking about are things like getting married/divorced, making a baby, moving to Alaska to build a cabin, etc. Then afterwards they find that the change didn't make them any happier! Now, they are not only unhappy, but they have now committed themselves to something that they can't just get rid of (a baby) or can't recoup their investment from (cabin in Alaska).

I think that one should go out and do something that absolutely scares the hell out of them, preferably something that's not permanent or destructive. If you step outside that comfort zone where you can get the adrenaline going and actually FEEL alive, then you can experience the contrast between where you are now and where you could be. For some that's bungee jumping, or skydiving, or facing up to their worst fear (flying, scuba diving, etc). Others go experience the "other" side of life, like volunteering at a homeless shelter or something that takes you completely away from who you usually are and makes you stretch your abilities.

Change is good!

Being screened for depression is also something to think about. My wife encouraged me to get checked a few years ago when I was in a real deep rut. With treatment and counseling I was able to get up off the floor, get a better job, go back to school, and be able to live again. There's no magic pill, and it's still a daily struggle, but the difference in who I was and who I am now is amazing.