I had my head cast once...
ONCE!
Seriously, it isn't as bad as you might think as long as you wear a bald
cap to protect you hair and put some vaseline or Nivea (just like the pros use) on your eyebrows and facial hair. My face was clean shaven so if you aren't I guess you'd need to load up your beard or mutton chops with nivea as well.
Most important is the method of getting air to your nose or mouth while the mold sets. Remember: McDonalds has the largers diameter straws. You really REALLY want to be comfortable for that.
Drag an old reclining chair out side (or into your work space) and cover it with plastic tarps. Simply tilting you head back can distort your jaw & throat line and will have a big effect on how the resultant positive cast and any prosthetics appliances made from it will look and fit, but so long as you have 'greased up' sufficiently getting the mold off when its done is no big deal.
Some of you non-pros may be intersted in my experience which happened when I was 18 and we needed a facial appliance to make me look old enough to play Ebenezer Scrooge. Sombody found this guy named Dan Platt, He was big into horror make up and had done a lot of reader contributor stuff to Fangoria back in the 80's. Our Jacob Marley was truly a walking nightmare. Dan went on to do some work on T2.
Neck distortion was the problem with my appliance. Dan decided it would be easiest for me to only have a single one piece appliance. He later swore he'd never do that again, because the odd angle that I tilted my head while in the mold caused the neck and chin to never quite fit right to my face when it was cast in foam rubber. I spent a lot of time on stage "thougthfully stroking my chin" to cover up the fact that I constantly had to push it back on. It was a bit stiff and the sculpted scowl made it really hard to smile during the final scenes. I had to learn to only lower my bottom lip to show my teeth in a grin that would have made Montgomery Burns shudder. Dan only made 4 masks for the 6 show run, which menat I had to be careful removing the makeup each night to ensiure I had one for closing night. This process was made extra fun due to the fact that was no hot water (and hardly any heat for that matter) in the dressing rooms. Less than ideal circumstances but I managed to make it through the run without using mask number 4.
I am NOT looking forward to having my whole head cast. My deep fear is that my eyebrows will end up all ripped out! :confused