The tendency to fall asleep? Well, we don't want you to stay awake, but one trick when you're doing the Compassion/Lovingkindness meditation before going to sleep, when you're lying down, is to leave the covers off, until you've finished the meditation. Then when you've finished the meditation, put the covers on and then you allow yourself to fall sleep. That's one way to do it.
Steve's very good at this. He will lie down and get in a posture that is not his normal sleeping posture. He lies down, relaxes, but he doesn't have the covers on. When he's finished with doing the Compassion/Lovingkindness meditation, he changes into his sleeping posture and then puts the covers on. He's usually asleep in about two seconds.