I work in Theatre Recovery and can answer some of these questions .
Firstly in regard to the bladder issue - you are laid down during surgery meaning that it’s much easier for fluid to return to the circulation from the extremities - mainly legs so this results in your bladder filling up . Also the Anaesthetist might have put you on an intravenous drip while you were in surgery to prevent you getting dehydrated / electrolyte imbalance which can be an unwanted complication of fasting and could slow your recovery or cause other problems . You may not remember having a drip but if you did then it would probably have been connected after you went to sleep and may have been taken away again just before you woke .
Obviously I don’t know what drugs you received but they all cause the muscles to relax to an extent which can lead to your bladder emptying itself - particularly if you then cough on waking as many people do. I’ve been doing my job for a long time and though it didn’t happen to me I know it can happen to anybody and where I work we just accept that it happens and get on with making our patients feel dry and clean and comfortable again - please don’t be embarrassed .
Though it didn’t happen to me both times I’ve had surgery I’ve been absolutely desperate for a wee just afterwards - in one case I had to convince a nurse that I really did need to wee , that it wasn’t just a sensation caused by my Gynae surgery . That time she wouldn’t let me walk to the toilet as I was still too wobbly - I had to use a commode and I practically filled it despite the fact that a male visitor had snuck into the bay to visit the patient in the next bed ( he was swiftly ejected again by the ward sister ).
The stuff on your forehead / in your hair . The Anaesthetist sometimes puts little sticky tabs onto your forehead attached to a little machine that helps to measure your sedation level . It does leave a bit of a grainy / sugary residue as you describe.
As to your wound - I know they can sometimes find the nodes using the same incision that they have already made to remove the tumour - I don’t know about the other way around . If you have more questions write them down to ask your surgeon at your appointment - it’s very difficult to remember everything after an anaesthetic and it’s best to lay any doubts you have to rest as otherwise they can continue to niggle at you.
Hope your recovery goes well and best wishes for your results xx