The person will be reluctant to admit, often times, the feelings are gone because he doesn't know how that's possible. Mood swings will be more shallow and less frequent if you've taken out a big stress. Do this for any upsetting feelings a person can bring up by thinking back in time. 3 times as before and test for residual feelings. It MUST be over and done with.
Current stresses are harder to work with.
Persons on drugs may not respond because they can't get into the feelings due to whatever drug is used to keep down their emotions. This simple therapy was derived from many years experience doing hypnoanalysis, most of the deep trance phenomena of hypnosis, and studying faith healers. It contains the essential elements for mental and some physical healing. You don't need to understand this method to make it work. The method is called suggestion with a trigger.