Wisdom Teachings - Sat Yoga, Costa Rica

Student Question:  Sometimes when I sit down and start meditating I try to focus on my heartbeat in order to get into a state.  After a while I forget about my heart and start feeling my forehead getting heavy and it feels like my body goes to sleep and then all I can feel is that point on my forehead.  I am wondering what is happening to me and whether it is normal or whether it is some kind of identification with my body and why is it happening if I really want to focus on my heart?