Strange thing I can do with my nervous system can anyone relate or explain what's actually happening?

TL DR: If I sit still and do what feels like 'internally tensing' up I can increase my heart rate on command. Im not flexing or tensing any actual outside muscle I know of. Info about me: I'm 20M, 6ft, 140lbs, white, no medical issues, on no medications, drink a few times a month, no smoking or drug use other than weed very rarely, and I live in the great country of Canada! I have zero medical or neuroscience training. I've been able to do this my whole life and always assumed it was normal until I realized I've never once heard anyone mention doing it themselves. I finally tried looking into it got some buzzwords from AI like "Voluntary Sympathetic Activation" but when I looked online and hit a wall, so I'm hoping someone here might have some insight. What I can do: If I sit completely still and focus, I can trigger this internal "tension" that isn't muscular. It's really hard to describe it feels like I'm tensing something deeper than muscle, almost like my nervous system itself. The sensation builds and intensifies the longer I hold it, but I can only sustain it for maybe 10 seconds max before it becomes too hard to focus on and do. I feel a bit of pressure in my chest when I do it, and It's strangely calming and relaxing for my actual muscles, but at the same time, it's almost too much to handle. and no its NOT a sexual feeling, which I know it might sound like. \- My heart rate spikes significantly, even though I'm completely stil, l comparable to climbing stairs \- I can't inhale/exhale while holding it; I have to focus entirely on maintaining the tension \- When I stop focusing or "release the tension", I'm out of breath and my heart rate slowly drops Something I noticed recently: I've been practicing more and realized I can kind of direct this sensation to specific areas. \- If I channel it in my legs\* it's deeply calming. My heart rate stays normal. I feel heavy and grounded. An AI I described this to (DeepSeek) suggested this might be parasympathetic activation rest-and-digest stuff. \- If I channel it in my \*\*chest or whole body\*\*, I get the heart rate increase, breathlessness, and overwhelming intensity. DeepSeek said this sounds like sympathetic activation—fight-or-flight, but voluntarily triggered with no external stressor. I can choose which one happens based on where I "aim" the sensation. I have no idea if that's even supposed to be possible. I spent a while looking on YouTube and PubMed. All I could find was either: \- Basic educational content about how the nervous system works \- Stuff about controlled breathing, cold exposure, or meditation, or the Wim Hoff Method \- Research on frisson/chills triggered by music or emotional moments None of it described what I'm doing. Everything I found required some external stimulus like music, temperature change, breathing techniques or just explained autonomic functions without mentioning voluntary control. I tried several search terms and dug through quite a few papers, but I genuinely couldn't find anything about doing this solely with the mind, while completely still, with no trigger. I also read that Buddhist monks do a lot of meditation and training like this but there is extremely little written about it that I could find and they only really talk about "focusing their mind" which is a bit of what I'm doing but I dont know if they are having the same effects as me? What I'm hoping to learn: 1. What am I actually controlling here? What tissue, what pathway, what mechanism? 2. Has anyone else experienced this or heard of it? 3. Is there an actual name for this phenomenon? 4. Are there any studies even obscure ones on people who can do this? 5. Is this safe to do regularly? It doesn't feel bad, but I honestly don't know. 6. Could this even be studied? Like would researchers be interested or is this just a weird quirk? 7. Any ideas what this could be useful for? I have no practical application for this, just curiosity. I know this sounds strange. I'm not claiming anything impressive or supernatural I'm genuinely confused and just want to understand what's happening in my own body. If anyone has even just a keyword to search or is able to do it too that would be super cool. I'm going to post this in a few subreddits that I think are relevant. Thank you for reading! I would love to get to the bottom of this with your help!