Laska last night was fine - Perky and annoying and spastic and typically crazy. Today? She's sleeping. A lot. She's just... a lump. Sleeping, not really playing, just sort of blah. I have an easier time telling with cats or dogs that something is definitely wrong (wet vs dry nose, etc), and I'm trying to figure out if weasels can just have a day where they sleep a larger amount than other days. Should I give it another day and see what she's doing tomorrow?

I'd wait a day and see.

I've noticed a difference in energy levels based on time of day as well.  Not sure if you are taking Laska out during a time when she is usually sleeping.