I agree, sometimes it is beyond our control. I prepare myself and my schedule for the chance that I might need more down time. I amp up self-care:
time-boxing,
pampering,
solitary walks,
scheduling an extra therapy session (by video-chat if necessary),
getting organized by checking my calendar and re-setting/starting my routines,
contact a friend or parent to let them know I might need a few getting-in-touch check-up phone calls until it passes,
canceling or rescheduling any unnecessary calendar or todo items,
make a grocery list and set up an instacart order,

Sometimes I've been able to weather through it because of these things. Also, when I 're-surface' the first thing I do is prepare anything I can for the next time, think through things which I might have missed getting prepared for last time.

Depression can be cyclic. Down for days then up again. It doesn't necessarily mean you are manic. I is just a symptom of this beast. I try deep breathing, meditation and exercise. When I feel a low period coming on I try to address what might be bringing me down. Sometimes I can't and seek out someone to talk to who understands. Talking about my depression helps me work it out. Writing things down also gives me perspective to see what is going on with me at that time. Don't forget, we are here for you.
Adding you to my team XX

Get away if it is someone making you get you depressed, walk,away, cause you don't need to be around those that make you feel that way or anything that is trying to make you feel bad!

Walk away.

Usually if im up to it, i force myself to either workout, breath, read the bible, write poetry.. And thats only sometimes i can... Sometimes i just wait until and if it passes..