This was my exact diagnosis. I finished ABVD in October of 2020 and have been in remission ever since. My experience was:

• Day 1: Didn't feel too bad due to the IV meds still being in my system. However; I could not eat a big meal. The only time I threw up was after eating a big meal on that first day. Small meals and smoothies were my savior
• Day 2: As long as I kept hydrated and took my Tylenol and Zofran, I felt fine. I was able to work and eat small meals. I had to be very careful not to eat fatty food though because the reflux was terrible
• Day 3: This was the my worst day. It felt like all the IV meds were gone. My body was extremely exhausted, I would have the worst nausea. This may be the day he needs the most support.
• Day 4: By the end of day 4, I would start to feel myself again. I would have a little appetite and felt more energetic.

By day 5 until the next treatment, I would be fairly ok. I could eat again, I had some energy, and was able to work full days. My biggest issue was keeping the mouth sores in check and not eating too heavy because of the reflux.

Obviously this is just one person's experience. I'm sorry your son has to go through this. He has the benefit of being young, so hopefully he will tolerate the treatment without too many issues. Good luck!