I'm scheduled for blood work tomorrow, so I have to fast tonight. I'm wondering if it's ok to take a sleeping pill before bed?

Safest is: ask them. Call the lab/hospital and ask or if you're too late, see if you really need it - don't take it if not necessary. Lastly - if you do take one - describe exactly what it is and when you took it (with water only) before they do the tests. Best wishes.