I think you'll find the answer behind the wall! We had a problem with rotten wood behind our tub enclosure and found that the surround was installed improperly and water from the shower was leaking behind it causing the wood to rot. There could also be a problem with the Plumbing behind your wall - there could be a leaky pipe causing the problem.
Something you ate was rotten
Cause its burnt.
It is much safer to take a bath than a shower cause in the shower you can slip so I would bath
Presence of sulphur.
Seats in the main valve body are leaking by, allowing water to go to the shower head.
No. Sounds like the catalytic converter is going bad. Rotten egg smell is a sign
Technically it could be on the other side of the shower wall, but common sense would tell you this is not a good idea.
full block of main drain. shower is lowest open area for back up to occur.
you have trash in your line take the shower head off and remove trash or possibly in water valve at shower
It would have to be the controls or the shower head. Distance from the heater or size of supply lines shouldn't have much affect. The only variable would be the control or shower head and either one could have a flow restrictor in it or both.
Poor water conditions and severe stress.
Cotton gets wet. By the end of your shower, a cotton curtain would be drenched and would fail to serve its purpose.