These sahm years came rushing back, in a rather tongue in cheek backward glance, when I read the summary of a recent study by the National Survey on Drug Use and Health. You can also read a summary here. This survey looked at rates of depression among various occupations. Major depression was reported most frequently in the following four types of jobs: Personal Care and Service, Food Prep and Serving, Social Services, and Health Care. Yep, that about covered it.
This isn't to say, of course, that there aren't plenty of moms (and dads) who feel great being a sah parent. More power to them. But for me, it wasn't a good fit. I was happier working and I believe my kids are better for it, too.