This happened to me a lot when I was lucid. Sometimes it'd be like I was walking in tar or something, everything is so slow; and when I tried running it's like I have to push off the ground so hard in order to propel myself forwards. It would happen at random times though, not just when I'm close to waking up.

So I stared imagining that I'm running on a conveyor belt, like a treadmill, except it's going in the same direction that I am. Like those moving walkways at the airport. I imagine the regular ground having that kind of motion to it. The physical ground never movies, but if you picture the sensation of it going forwards it helps. It works really well for me.