What Causes Tightness In Chest And Shortness Of Breath?

Question: Hi, I'm 27, male, 158lbs 5"11 non smoker or drinker. I have had a reoccurring issue while sitting at work, on the couch at home, and sitting in a resturaunt on 4 occasions where my lower neck at my XXXXXXX apple or lower on the sides starts to feel tight. While that feeling progresses I notice breathing through my nose seems limited or restricted. Similar to if you turned your head far left or right and tried breathing, it is harder. It seems to progress within a few minutes. If I breathe through my mouth it seems better. I have felt my pulse on each occasion and it typically feels weak and slow, I would guess in the 48-52 bpm range. On one occurance in the past my phone read 56 bpm, 54 bpm, 30 bpm (assume it read correctly which may not have) when I checked my heart rate, I did not use my phone in this recent case. I start to begin panicking and think my heart will continue to slow until it stops. My heart will beat faster immediately as I become in fear and the tighness in my neck/throat goes away and can breath through my nose with ease. I believe I may have gerd per past Dr visits however I want to note I don't feel any burning sensation when I experience these situations. It is just odd and frustration because after I go through my breif panic, and become fine afterwards, I seem to be ok after that, going a week or two before it happens again. I've been in fear as well if it's some kind of freak arrythmia or issue that may cause sudden death syndrome despite things returning to normal. I have had ekgs, an echo, and stress test that came back ok from the cardiologist in July and prior. The fact that this seemingly random issue keeps causing again concern as something else may be wrong. Are there likely issues and or a reasonable explanation for this? This puts the fear of death in me and it doesn't happen often enough thankfully, to where a Dr can observe it. I appreciate your help.

-XXXX

Thank you for the response. I did have a chest xray in April which was clear. I do want to just note that I get the symptoms prior to becoming alarmed. I will requests those other tests as I think it would help narrow down or find the cause. I can exercise and do things without issue, this just seems to happen every couple weeks when I'm sitting and on one occasion partly standing. my last potassium test last month had me at 3.5 which I'm curious if that could be a factor.

Thank you again!

Thanks and one last question, are strong responses to standing up after sitting where my upper abdomen/lower chest noticeably tightens when shifting to stand and walk after rest normal? it sometimes is unnoticeable and others it feels like pushing while going to the bathroom. I have had a bit of anxiety at this point and loose stools since the event. I'm not sure if it is related.