According to the description for the Heal skill used for the purpose of treating disease, it is unclear if a person can do a Heal check on himself, or if the person doing the Heal check has to be someone other than the diseased person. From the DMG, pg. 50:
Second question, if you maintain the disease state during your first extended rest after being infected, do you continue to apply the initial effects of the disease?
From the PHB, pg. 185An ally can use a Heal check in place of your Endurance check to help you recover from a disease as described in the PHB.
As I think it's been established when powers use the term "ally" it doesn't include the character using the power, I believe that there is a case that the heal check from an ally suggests that it also cannot be done by the diseased character to treat his own disease.Treat disease: Part of the diseased character's extended rest. You must attend the character periodically throughout the extended rest, and you make your Heal check when the rest ends.
Second question, if you maintain the disease state during your first extended rest after being infected, do you continue to apply the initial effects of the disease?