There are a few things that can cause your cat to drool excessively.
Cats will drool if they feel nauseated but not to the point of vomiting.
They will also drool if they have mouth pain from a possible tooth or gum problem. Take a look in his mouth but you might not see anything. Sometimes tooth pain is not noticeable.
Sometimes they will drool if they have ingested garbage or other irritants and will drool if they have ingested poison.
Is your cat a male? Is there a female in heat somewhere nearby? If so, this could cause your cat to get really excited and drool because of it.
If this just started, you can just watch it and see if it gets better on its own.
If not, a vet could quickly diagnose it for you. It's an emergency is he is showing any neurological symptoms (falling over, stumbling, not focusing...)
The hair loss might be because of a thyroid condition, allergy, skin infection.... Your vet can help you with this problem at the same appointment.
Let me know if you have more questions.