Why do i feel so depressed after lots of activity with other people?

Are you a natural: introvert? Introverts generally feel drained by excessive social contact, whereas extroverts feel energized. Or, maybe you're just going on 20 mile hikes with your group, in which case you're not depressed--just really, really tired (smile). If the symptom persists, see a family MD or psychologist.

Great input by Dr.: Griggs. It could be exhaustion or in some cases - it can be a major let down after a remarkably good time.