Just posting here to get some insight into what happened and whether or not it's something to cause concern. Not terribly worried about it, though, as there's no pain or discomfort or anything, really.

So the other night I was sitting on the couch watching Netflix and went to stretch. One of those morning kind of stretches where you reach up above your head with your arms. Since I was sitting on the couch, I kinda arched my upper back over the back of the couch and it felt great because I really stretched and elongated my chest. But then I felt a pop kinda near my sternum, maybe the lower end of my rib cage in the front. After the pop was a strange kind of cooling sensation in the area. There wasn't any pain at all, but it felt "weird". I can't figure out how to describe it, but it felt like something was out of place. The other weird thing is it almost seemed like I could breath easier and had a bigger lung capacity. But that might have been in my head.

Then, maybe a half hour to an hour later, I flexed my lats, as if I were pulling my shoulders down towards the ground, and I could feel another little click and it seemed like whatever it was that "popped out" went back, and everything felt normal again. No pain or soreness at any time, though I probably ought to mention I had consumed cannabis, so it may have dulled any pain that would have been present. I had also lifted earlier that day if it matters (squat, overhead press, deadlift).

It may or may not be related, but I'm currently working on correcting my posture, as I have what a lot of people get when they do a lot of bench press, where my shoulders kinda slump forward and my chest closes off instead of being open.

Any idea what it was? Is it possible to pop your sternum or a rib out of place without terrible pain? Or is there a tendon that maybe slid over something? Maybe something with a piece of cartilage?