My husband has stage 4 esophageal. He's done all his chemo and radiation outpatient. The times he was hospitalized were for low blood counts (needing transfusion) and for blood clots. Are your doctors treating him for something specific? Usually, after chemo, they give a cocktail of meds to help with nausea, energy, etc. For my husband, he's usually wiped out the first day, then ok, then really nauseated about day 3-4 after his treatment.
I think you need to ask the doctors what's going on. 3 weeks bed ridden and out of breath doing normal hygeine sounds like more than just chemo reaction. Is he eating at all? Getting proper nutrition is vital. Is his pain level treated? Pain can cause a lot of problems if it's not addressed.
Hope things look better soon.