Smzclark; Addiction is created when one repetitively and compulsively uses something like a drug, alcohol (also a drug) or some other form of stimulant. Each time they repeat it they build a deeper imprint of the neurological circuit. It is much like drawing a line and then tracing over it again and again making it darker and deeper with each pass. Remember that underlying all of our complexities we are basically an electronic device. By that I mean that our thoughts and senses are electrical impulses that travel along neurons.
When one quits an addiction it is like ripping out a wire in a circuit board. The board may function without that wire but in the case of something as complex and finely tuned as out brain it is bound to have repercussions.
Often our subconscious begins seeking a replacement for that stimulus. Neurologists have done brain mapping and found that religion give a return quite similar to drugs.
It is most likely that your friend has, more or less, simply switched "drugs" to get that sensation.
Your friend should adjust to the change away from addiction and level out but he might also simply plunge deeper into his new addiction.
Of course this is an oversimplification if you want a fuller understanding research neuropathology and addiction.
In a nutshell it is a form of psycosis... sort of. A psychosis is a break from reality, so its not quite the same thing.