You should try to be as comfortable as possible when you MILD or use autosuggestion like that. You want to fall asleep pretty quickly, so lie in whatever position you normally use to fall asleep.

There is a big difference between MILD and WILD. In a MILD, you are just trying to remind yourself to become lucid as you fall asleep. The idea is to remind yourself of lucid dreaming and imagining yourself becoming lucid as you fall asleep. In a WILD, you are trying to get yourself into a trance-like state and hold onto some awareness as you pass directly into a dream. It sounds like you were doing a hybrid of the two, which just ended up keeping you awake way too long.