I feel mostly-fine today besides fatigue and brain fog, but they're still within normal variability of my normal healthy days. Except I just have a sense that I'm getting sick, if that makes sense? Can't put my finger on it, it just feels like there's something wrong with my body right now. Some vague atmosphere of physiological doom. Started shortly after waking up this morning. I cardio exercised quite hard last night with no issues.

Oura ring is showing slightly elevated sleeping heart rate last two nights, but still within normal variability.

By end of day tomorrow night, will I consider myself either sick or clearly coming down with something? Anything very mild, or still 'unclear' (like if I'm still tired with vague sick-feelings but with no other concrete symptoms), will resolve 'no.'

*update: going to bed now, am feeling much better than before