Sleep and energy levels are usually the first sign something's off for me, especially this time of year. I can sleep 16 hours and not have the energy to do my laundry for a month (ie past few months) and not feel traditionally depressed. Once that starts interfering with my life (not making it to class, not getting work done, people noticing my lack of clean clothes), the more traditional psychic symptoms start to show up in earnest.

It becomes a feedback loop for me. My lack of sleep/energy-based depression causes me to neglect my obligations to the point where it triggers my worthlessness/you're so stupid-based depression which then reinforces my energy-based depression.

Based off of personal experience, look into it. Might save you a lot of trouble.