Dear friend, welcome to HCM.
Passing out after a hot shower is commonly due to sudden vasodilation
( relaxation and dilatation of blood vessels ) where blood pools in dilated vessels and the BP drops.
Corrects on lying down or rest.
I think this is what heppening to you.
How long are you unconscious each time?
Right arm numbness
may be a circulation problem like a narrowed vessel or a nerve
Is there less sensation or tingling/ pain / altered sensation in the arm?
Avoid hot baths. lie down if feeling dizzy.
Please get evaluated for the arm problem.