It is like the current in a river, which pushes us if we flow with it, but opposes if we try to swim against it. So when we are with it, it works in our favor. When we go against it, it opposes us. In either case, it is His grace.
There can be sleepiness if you go very deep into meditation. I used to have this problem, and I wrote to Master about it. He answered back that as activity is the life of the body, some sort of inaction is the life of the soul. Therefore, when we go deep into meditation, the life of the soul takes over.