It is normal for them to act like they feel bad after being dipped. The will be sleepy and just act like they dont feel good. Normal self again???? You are wondering how long it will take for the condition to subside? I have seen it in one dip and I have seen a dog have to have several dips (5 or 6). It all depends on how bad the case is.
I do not use Mitoban dip for the treatment of demodectic/red mange because I have found greater success through other routes, but this is a very common dip. It is true that once dipped they will scratch it is from the mites moving and dying off. Alot of times the vet will give you something to take at home to help..... my favorite for this is Temeril-P, if it keeps up past the second day after dip give your vet a call and see if they can RX you some or something similiar.
Good luck and by the way Welcome!