Any question answered...

Meh.

If you are in fact recovering from something you should just be riding your bike. Out in the sun. For as long or as short as you feel up to it.

Turbo training and associated worrying about numbers of this or that is likely to just cause anxiety and cause you to push harder until you make yourself sick again.

Spot on.

Like I said just the commuting & social pootling is plenty really. "training" should only be done when back at full strength. Some shortcuts can be taken to get there. Like being aggressive with the commuting, eating/sleeping well etc..

My previous recommendation for throwing in a bit of leg exercises might be redundant if there is only 4 weeks. Might just end up with leg fatigue!

Listen to hippy, get out and enjoy yourself on a bike. Consider this an active recovery rest period, you'll only go backwards if you force yourself now. No "training" !