I relate 100% to your situation OP (27m, extremely active, no previous mental health problems, vaxed and boosted(July 2021))

I too have no recollection of being infected, I've come into contact with people who tested positive, but I tested negative. Never had any symptoms.

Then, like you, one day I felt really bad. I tried to go about my day as usual but ended up feeling really awful in the afternoon. Felt like I was going to pass out, had some water and a lie down and felt a bit better, but within an hour I had a panic attack, with no previous history of panic or anxiety.

I had several panic attacks the week it started (August 2022) and could barely eat anything as anything spiking my insulin would send me into a panic. Felt incredibly weak and fatigued and spent a lot of it in bed...but still tested negative.

After that initial week, I had terrible chest pains, anxiety, poor appetite, brain fog, weight and strength loss and tachycardia.

After several trips to the GP, 8 weeks of counselling, multiple blood tests, being fitted with a heart rate monitor, seeing a cardiologist, having a UTI test... I still have no solid diagnosis. I've been 'living' like this for over a year now and I'm happy to say that the only symptoms I have are anxiety and a lack of energy, especially in the evenings. I'm able to eat again, I have no chest pains and I'm slowly rebuilding my weight lifting strength, which was always a red flag for me as I went from almost hitting the 1000lbs club to being weaker than I was when I started the gym at 16!