Why are hypnic jerks so random?

[BeeClock]

Sometimes I would go several weeks without experiencing any hypnic jerks, then one night I had about a dozen hypnic jerks. I do not remember having had any since then. Why is this? Hynpic jerks are caused by being almost in sleep paralysis, and when that occurs one no longer feels their physical body, which results in the sensation of falling. So why did I have so many while falling asleep one night, and rarely experience them otherwise?

[ShadowOfSelf]

Im not sure, did you go to sleep late?

[BeeClock]

I can't remember. I think I went to bed at my usual time.