Stop worrying about EVERYTHING. I like being a hypochrondiac as much as the next guy, but honestly, go to WebMD or medical forums.
But if you want my medical advice, you may have a muscle cramp. Eat some potassium and don't do constant anaerobic activities. Or it may be a strained muscle due to your awkward positioning. Get a massage or take a hot bath.
Kimi wa ne tashika ni ano toki watashi no soba ni ita
Itsudatte itsudatte itsudatte
Sugu yoko de waratteita
Nakushitemo torimodosu kimi wo
I will never leave you