Tachycardia during workouts

I am a 44 year old white man. I am in great shape 172cm/69kg, I do heavy weight training 6 days a week on a push/pull/legs split. I am on testosterone replacement therapy and take IM injections twice a week. Since May 2025 I stated having episodes of tachycardia during my workouts where the HR will shoot up to 170-190 BPM and hang there despite stopping activity. It will sometimes last up 30 minutes. I don’t feel otherwise unwell during these episodes. I can feel my heart pounding but I don’t feel overly lightheaded or short of breath or anything like that. I have experimented with Valsalva maneuvers like holding my breath for a little bit, exhaling and then rocking back with my legs up. This has been effective sometimes but is difficult to do solo. These episodes have been occurring now 3-5 times per month. I have seen the GP, and they didn’t seem worried. They did blood tests including cholesterol, urea and electrolytes and all was normal. They also did an ECG which was also normal. I’ve contacted them again and they agreed to put a 24 hour monitor on. My concern now is that I can’t force an episode so it’s just going to come back normal presumably and then I’ll be back at square one. Thanks for your advice and if you need any clarifications please let me know.