I have a plausible explanation for Pres. Biden's recent trouble and obvious return to vigor.

[Metaphorical]

2. I have Sleep Apnia

I have had a couple of myocardial infarctions over the years, and suffer from COPD - Chronic Obstructive Pulmonary Disease - that eventually put me into the hospital for a week. Until it was treated, I was getting about 85-90% of the oxygen that I needed during the day, was constantly tired, and was reaching the point where even crossing the room became a struggle. I started on a CPAP machine, a large, coupled with an oxygen pump (the latter of which is VERY noisy and weighs enough to be difficult to move around).

The CPAP machine + oxygen + a boatload of drugs has helped dramatically, but it comes with its own problems:
* Dizziness
* Frequent laryngitis and hoarseness
* The need to urinate frequently during the night (primarily due to Furocimide)
* A soft voice (my voice is naturally quiet, but this exacerbates it)
* I wake up energized, but by early evening I'm struggling to stay alert, and definitely need my oxygen.
* I tire more easily than I used to
* Colds can prove difficult, because CPAP typically uses a nose clip that requires clear nasal passageways.

I'm relatively young (early 60s). I had not heard that Biden had sleep apnea, but once that was raised it made a great deal of sense. Especially if he had been doing a lot of air travel and was sick, all of the symptoms could be explained this way. Note that it has not changed my own mental acuity once it was treated, but the COPD had a major negative impact as a writer and programmer, and it took me almost two months to recover even after being in the hospital.