While there's nothing in the literature (or my experience) to suggest Akineton might cause damage to the endorphine-producing mechanism, it may well depress this as well as other things, on a temporary basis. It may also be that changing/discontinuing the drug has thrown off your perception of well being, and this may or may not be a transient effect of withdrawal from the drug. Since you say you've been off it "for some time" I'm suspecting this is more an essential problem than anything caused by the drug. I'd discuss this with the psychiatrist and look into other possible causes and/or meanings of this strange development. Meanwhile continue to exercise and perhaps eventually the experience will begin to once again feel as it should.
I hope this is helpful. Good luck to you.
John Kenyon, EMT, CCT
Non-invasive cardiology tech, Emergency and Critical Care technician, Critical Incident Stress Mgmt. specialist