I've had quite a few SP episodes before and realized that the majority of them happened when I was in a relatively cool room. Not "comfortably cool", but cool as in "okay, it's kinda hard to fall asleep because the air around me is chilly." It's that temperature where you just want to get a big blanket, wrap yourself in it, and curl up in bed or on the couch.

If you're stuck on getting to SP and don't know where to start, try lowering the thermostat to a temperature that's just bearable.