Weather conditions seem to affect me. It seems that if there is a storm coming in, I will become inexplicably depressed. The depression almost always lifts hours before it starts to rain.
I suspect diet can have a strong influence on mood. Lately I have been eating way more cheese and other high fat foods and I have had less energy for the past week or so. That has made me lethargic and I have had a hard time keeping my interest on anything.
This is highly specific, but if you take Melatonin to help you sleep, only take it at the time you would normally go to sleep. If you can't sleep and take it a few hours after your normal bed time, you may wake up the next morning feeling fine, only to become extremely depressed within an hour of waking. Anyway, that kept happening to me until I noticed the correlation and stopped taking Melatonin outside of my sleep cycle - Since then I haven't had that specific kind of depression.)
_________________
Never let the weeds get higher than the garden,
Always keep a sapphire in your mind.
(Tom Waits "Get Behind the Mule")