Feeling Faint Late At Night Again

I feel it right now -- I have that kind of tiredness where I feel my head is really heavy, and that I am barely hanging onto consciousness.  It's the type of fatigue where I can instantly pass out at any time.  If I'm holding something, I could pass out and drop it.  If I'm standing up, I could pass out and fall right where I stand.  It's that kind of tired.

Have any of you felt tired like that?  I felt that some time ago, but it went away, but now I felt it last night and now.  Don't know why.  I'm scared this is a foreshadowing of sundowning and how Grandmother turned into a demented monster come dusk.  Hope this isn't an omen.

Still need to power through, though.  Have some things I still should do.