If you fall asleep, its ok. But you may miss blessing some part of your life which you want to if thats your wish.
When we do blessing meditation it should be from our heart and not as a compulsion.
We are enhancing our blessings with VK.
You can please do it in daytime when you don’t have the pressure for next task ideally.
Any meditation should be done when you are free and not in a hurry.
I fall asleep many times in meditation even when its daytime, thats ok. I guess VK knows that we need to go into deeper level within sleep. So it manifests sleep …..