My method is to stare into the blackness. I let my mind wander into whatever it will, and as soon as I start feeling REALLY tired I start to focus on the swirling black shapes. Really, it isn't blackness, and there are all kinds of cool colors and faces and stuff swirling around (go ahead, close your eyes now and try to tell me its all just black!). I usually feel some deep, heavy pull at this point, telling me I'm getting close to the dream world, and I will either get excited and pull back to reality or keep relaxed and fall into the dream.

The key for me is focusing on the shapes. This way, my mind isn't working too hard (i.e. methodically counting and waiting - I don't think that would work for me, too regimented and mathematical), but passively observing the cool pictures keeps me consciously engaged while my body completely relaxes. I think the "heavy almost to hurting" sensation you describe is like my "deep, heavy pull." You're probably getting close! When you feel that "different" sensation (you know what I mean), just try to relax and go with it. If you perk up and become more alert, which is the knee-jerk reaction, you'll end up waking yoursef up.