27/f, healthy.. chest pains

I know your first response is probably "go to the doctors"... but anyone I've told about this never takes me seriously because it makes no sense for me to be having these symptoms

But basically, if I am lying in bed for too long, (over maybe 10 hours) I get severe chest pains. This has been happening for years and has always gone away after I am upright for a while. Until today. I was having chest pains for a good 6 hours.

I am in fairly good shape, don't do drugs.

Can anyone tell me what might be causing this?