Regarding your friend, to be honest... if they thought you were joking, then maybe they are not the friend you thought.....
or maybe they needed to be told that this wasn't a joke and its how you really feel.
If I may ask, have there been any life tradigys ?
I mean like family members passing on? or have you been cheated on by an ex recently?
Regardless of not knowing why you feel the way you do, there is always a route to the problem. It's never good exploring what this maybe, but the is always a cause.