why do the sparks fly off from our body when woollens are taken off in dark?

Answer 1

Sparks fly off, whether or not in the dark, you can see them in the dark that's all.

This is because of static electricity. When you wear woollen clothes, due to the repeated rubbing between your body and the cloth, there's a transfer of charge (electrons) and when you try to take it off, they try to get back to their original positions (discharge action)

This transfer of electrons is nothing but electricity and they are the sparks that you saw

Answer 2

It's the result of static electricty.