Your father needs to swallow every day to keep the swallowing muscles active. Believe it or not, those muscles can very quickly forget how to work and he would have bigger issues later on relearning how to swallow.

I know its really hard for him right now but he must get his nutrition and hydration. If he isnt taking in enough talk to his doc and ask for him to get hydrated. They will give him a couple bags of saline and he will instantly feel alot better. Nutrition and hydration are very important and must be top priority here. Every single day he needs 2500 calories and 48 oz of water, no skimping. Getting to take more than that is even better and he will feel better too. Ask for a nasal tube to help, its a great temporary measure to get him thru a bad few weeks. Also anti-nausea meds like zofran can help with his nausea. He should take the meds around the clock as once you fall behind and are nauseous, its next to impossible to catch up. That will turn into a huge cycle where his nutrition and hydration will not be enough and he will get sicker and sicker. Very quickly this can turn into malnutrition and dehydration and require hospitalization. Pay very close attention to your fathers intake as malnutrition and dehydration are things not to mess around with. I am speaking from experience, i ended up being hospitalized a few times for this and I felt so bad I actually thought i was dying. If you feel your fathers health needs medical attention, take him to the ER where he can get hydrated.

best wishes!!!!