@askmehowiknow
Teachers surely aren't intending to 'get signed off' with a medical condition to mean they don't have to work. Is that really true?
This isn't me, btw, I'll be in work as usual in september, but...
Imagine you have been told to shield from March to August 1st. Not allowed to leave your house/garden. Told to get someone else to put the bins out for you, as it's too risky to do this basic task.
Then 1 month later you are expected to be in a building where almost 2000 people mix freely, where it is impossible to keep 2m away from others. You will be in a poorly ventilated room with 5x30 adolescents for an hour at a time. No masks, no visors, no screens. No mitigation of risk other than wash your hands (even though there's no sinks), stay away from other adults (who you normally only see for 20 minutes a day anyway) and massive bubbles that are rendered pointless by mosh-pit corridors, communal toilets with exceptionally bad hygiene and everyone coming on the same buses.
Do you not think in this situation you may actually be scared enough, that your stress levels could be high enough, that actually, a doctor could legitimately sign you off with stress?