Vania,

Could it be that something happened before you went to bed that you just do not remember? A bad impact just before going to bed would often not be remembered. Having amnesia of an impact is not uncommon and does not require a severe impact.

Unless you have violent seizures or other body jerking issues, you would not be moving fast enough to cause any sort of impact. But, as I said before, sleeping with your head pressed against the headboard could cause a lump, just from the prolonged contact. Anybody who has fallen asleep in the car with their head against the door post will likely have experienced the resulting lump and/or soreness.

I don't think people should be concerned about bumping their headboard in their sleep.