Me. Normally fit and well physician used to working 10 hour days knocked absolutely flat for 6 days, temp 40°C, worst ever headache, couldn't eat, so breathless I almost blacked out walking up a hill I can normally do in under 5 minutes.

This would be classed as "mild". https://twitter.com/australianpatr5/status/1274300047493001216

In the "moderate" category I've seen patients fitter than me, marathon runners, unable to breathe without oxygen, tripodding like a child in bed, pulling themselves forward to try and fill their lungs. Some have significant kidney and liver damage.

"Severe" would require high pressure oxygen masks, forcing oxygen into the lungs like if you had your head out the window of an InterCity train, with your mouth open.

When that doesn't work, patients have to be anaesthetised and mechanically ventilated.

Many never wake up.

"Critical" means they're on ICU, machines are doing their breathing for them and in some cases also filtering out urea and potentially toxic electrolytes in place of their kidneys. COVID patients often have blood so thick it clogs up the filters, again, and again.

Many patients at this stage are nursed "prone", on their front, to improve their breathing. This is a laborious process involving a whole team to turn them.

Sometimes the breathing tube becomes dislodged, and patients become dangerous low on oxygen.

Even those who do recover from critical face a long road to recovery, trying to rebuild their wasted muscles, their brains scrambled by delirium. Most will need physical rehab, the mental scars may never heal.

So yes, I do know some people who have had it. Hope it helps, mate.