A common side effect of many chemotherapy drugs but Methotrexate in particular is mucositis. You can get all the gory details in Wikipedia if you are so inclined but in summary it is is "the painful inflammation and ulceration of the mucous membranes lining the digestive tract". You get mouth sores. You get sores in your throat, and Alex has them there quite badly which makes drinking and eating pretty much impossible in the short term. Another characteristic is that the body produces a lot of sticky, thick saliva that clogs up the throat, makes one gag, and is just generally gross. It lasts three or four days.
How painful? Painful enough that Alex is on a continuous morphine drip to help cut the pain. He has also started getting nutrition intravenously as his weight is very low so the jungle vines of IV bags are hanging down once again.
Doctor figures we're here for another week.
Okay then.
