Exhausted won't eat

My dad was diagnosed with stage IV NSCLC in Dec 2016.  He started out on Ketruda and is worked really well until it started attacking his Kidneys.  He went through a several rounds of Chemo that  shrunk the cancer.  He now is only showing the cancer in the main original turmor that has shrunk and a little area close to that.  The Doc put him on maintenance therapy and he has had scans show the Cancer is stable and not growing. 

The maintance therapy seems to be much worse then the full chemo.  About five days after the infusion, he does not eat for 3 to 5 days and then sleeps at least 24-36 hrs.  During this time he looses around 10lbs.  Then gains it back before the next infusion.  His last few treatment side effects seem worse and he is scared it is more than the Chemo.   Normally, I do not see him in this state but the last few treatmens he was visiting me at my house when he started the sickness.  I don't know how to help him.  He seems really worried and I am too since I have not witnessed this before.    On Tues I was able to get a few bites of breakfast in him and nothing else.  He would nott drink until late afternoon when I begged to at least drink a coke to get some callories in his system.  

He is really hard headed and I don't want to make this worse on him but I am not sure when it is time to be worried.  His doc says that more immunotherapy will be in his future since he has and extremely high PDL1.  I am wondering if it may be time to ask the doc for break on treatment for a month to recover.  He did take a month off before and it seemed to help.  I am worried that the maintenance therapy may need to be adjusted but don't want him to make changes unless needed as long as the treatment is working.

Leslie