It started about 18 hours ago, but isn't constant. The spot is under my left breast but more towards my middle, a very small and specific area. It's a sort of stabbing sensation that lasts a second, then goes away for a second, then comes back for a second. It goes away entirely when I change position and take a few deep breaths. Last night it was appearing regardless of which side I was laying on, but laying on my back seemed the least likely to trigger it. It happened maybe 7 times over the 18 hours since it first started, but over that time I also slept and might have simply not noticed it in my sleep. I was hoping it would have been gone this morning, but it started again when I got up, although now the overall thing didn't last as long as yesterday.

I have anxiety and hypochondria but I can tell that this isn't a panic attack symptom because last night it kept appearing while I was 100% engrossed in a book. On the other hand today the fact that it's still there is making me anxious which might explain the next symptom - a very strong heart palpitation. I'm mentioning this in case it might be relevant but I do get heart palpitations with anxiety. Although this one felt particularly strong.