This is normal. It depends on how much of a snorter he was. It is hell for sure. If you are a casusal user it is a little easier. My son used all the time then went to crack. But, was able to stop on his own like in your case. Normally, an everyday user more then once a day, needs rehab. It is a tough road to get clean. But, if he is determined to stop, then he will stay clean. The temptation will always be there but, willpower is the key. And I agree that this is probably a systom of withdrawl.
I wish him the best of luck,
Carrie