So my question is mostly about whether or not I should go get checked out. Is this something I should worry about? Could I have some injury from years ago that I wasn't aware of? Or just rest it for a while and stop worrying? Sorry for the incoming novel, but I'm going to try to be as descriptive as possible.

This has actually happened once before. I posted about that incident here: (https://www.reddit.com/r/AskDocs/comments/590ayc/sternum_pop/) though I don't think I gave a good description. I don't know why I thought it was my sternum before, my only guess is it happened really quickly, kind of scared me and I didn't quite know what was going on, and I had also consumed cannabis, so my perception was certainly altered. As a matter of fact, this is the second time this has happened, and both times I had consumed cannabis, so that may or may not have something to do with it. Maybe a certain muscle is relaxing just enough to allow something to shift? I dunno.

Background info:

Age: 26

Sex: M

Height: 6'1"

Weight: 205lbs

Race: Caucasian

Duration of complaint: happened last night - and once before 5 months ago

Location (Geographic and on body): USA, area of concern is mid back

Any existing relevant medical issues (if any): N/A

Current medications (if any): just some doxycycline for acne

Other background info that may or may not be relevant: The past year I've been eating well, lifting weights, some running. I've lost over 100lbs. I've also recently added in pull-ups to my routine - I wonder if hanging and elongating my spine during pull-ups may have affected this. I've also always had terrible posture - neck craned forward, shoulders slumped forward. I've been actively trying to correct my posture.

Additionally, I have a friend who is a massage therapist, and one time when I was having a lot of mid back pain, I asked her to work on me. She thought I had a rib out of place, popped it, and the pain was immediately gone. May or may not be related.

Anyway, on to what happened. As I described in my previous post, I was on the couch, and kind of stretched, and felt a weird sort of pop/click, though I could definitely tell it was in my mid back area. I'll try to describe the stretch I was doing when it popped - I took a big breath in, had a straight back, maybe slightly arched in the upper back, and straightened my neck, using my neck muscles to push my head upward if that makes any sense. There wasn't any pain through any of this - not the pop, nor anything after.

When it popped, I definitely felt some kind of grinding in the area, and I felt "looser" though I also felt weird, like something definitely moved and felt out of place. It felt like something moved upward, and I felt "taller". Remembering what happened last time, I was able to squeeze my lats, pulling my shoulders down, felt another pop/click, and everything was back to normal again. Something moved downward, and I didn't feel "taller" anymore.

A bit later, I stretched again, and the pop/click happened again, and things felt "loose" and weird and "taller" again. Though this time I decided to leave it alone and not squeeze my lats to put it back to "normal". I noticed that my chest was "bigger" and more open. I took a deep breath, and noticed I could breath much deeper and expand my chest more. Before, it always felt like something stopped me from expanding my chest all the way and breathing as deep as I could. The first deep breath in, I did feel a series of pops as I expanded my chest all the way, but there was no pain and they stopped after the first one - almost as if my ribs or tendons were shifting to adjust to the new position? I dunno.

Now, just standing with minimal effort I am able to maintain a fairly decent posture. It took significant muscle effort before to get anything resembling good posture. My shoulders are now back without me actively pulling them back, my chest is bigger and more open, and my neck doesn't crane as much. While it does take a conscious muscular effort, I can now straighten my neck to a range I wasn't even able to reach before. I feel a little "taller" and less hunched.

I went to bed, and I don't feel as "loose" as I did last night, but I still feel like my chest is more open and I can expand it more, my shoulders are still sitting further back without effort, and I am still able to straighten my neck more than I used to. My muscles on the back of my neck are a little sore, though. Probably because I have been straightening my neck a lot since it happened, and they haven't been worked like this in who knows how many years.

I didn't go to urgent care because there wasn't any pain, and all-in-all I feel like something fixed itself. I am going to bring it up with a doctor whenever I can get an appointment, but I figured I'd ask here and see what all you smart reddit doctors think. It seems better now, but is this something I should worry about? Should I have an x-ray or something done to see what's going on? Sorry for the wall of text, but thanks for your help!