I was trying to FIRM the other day. It goes from floorwork to standing. I feel lightheaded when switching like that. Is there any reason that is happening and what could prevent it?

It's very normal to get light headed when going from the floor to standing ... Just take your time and make sure you keep your head up above your heart...

Also I would make sure to eat a little protein about a 30 min beforehand and drink LOTS of water!

I'll try that today.