I'd like to share one day's worth of experience with modafinil.

I noticed a huge difference in alertness. I was filled with an urge to be doing something every second. I don't believe I was more intelligent (some of the work I did that day turned out to be low quality) but I was much more productive. And happy. I felt like I was just "riding the day" -- that going through life, minute by minute, running errands, checking items off my to-do list, and seeing what happened next, was boundlessly fascinating.

I suspect that, at least for me, and maybe for others, most unhappiness is really fatigue, coupled with the guilt of not having accomplished much in a state of fatigue. Simply not being tired makes me deliriously happy. I am not surprised by the study that coffee reduces depression in women, though I know to be suspicious of medical study methodology. The symptoms of clinical depression look a lot like the symptoms of chronic sleep deprivation (fatigue, inability to concentrate, clumsiness, weight gain or weight loss, dramatic and irrational emotions). It's possible that some people with symptoms of depression are actually sleep deprived (or that a typical amount of sleep for a modern-day working or student life is too little for their biological needs.) I had a year when I thought I was losing my mind; in retrospect, it may have had something to do with getting no more than five hours of sleep a night.