My english isn't that good, and specially it doesn't come in handy right now to explain and ask about something with my collar bone.

So, the problem is that i was taking a shower and arched my back, randomly, and i felt that my two collar bones, specially the left one kinda "moved" and i felt a light pitching pain in my chest. It cut my breath for a second and then i felt that my entire left arm was a bit weak. I moved both my arms and it didn't hurt, i felt everything was normal. No fracture or any abnormal feeling or look in my bones. But then when i touched at the same time both of my collar bones, one hand to each one, i felt that my left collar bone was sunken or deeper than the other. I then touched the end in where the two bones meet at the center of the chest and neck and indeed, the left side was lower than the right and that's not normal for me because being an obsessed collar bone person (though you cant see them, im not that skinny) that i am, i could tell something was wrong there. It hurts when i touch my left bone and when i touch it i feel a light pain through my left side of the neck too.

Maybe is it a tighten muscle? A joint?