See questions above. 4) One that suffers from constant chronic pain such as arthritis, is he able to comply with the mitzva of Simcha during Yom Tov? Does he have to consume extra pain killers pills in order to comply with this mitzva?

There is a definite consideration to minimize anything that prevents joy and happiness during the days of Yom Tov. However firstly, the physician familiar with the patient’s condition should be consulted. Horav Shlomo Miller’s opinion is similar.