Yes, it can, and yes it's fairly common. A large proportion of CFS sufferers will regain a degree of functional ability, but then go on to get ill again. In these cases, the CFS follows what is called a 'relapse and remission' cycle. I had it for 3 months, then was totally in remission for 3 years. Then got it again, and had about 80% recovery for 4 years. Then got it again. In otherwords, I relapsed 3 times and had varying degree of remission inbetween.The relapses are usually triggered by something. In my case, it's viral infections. Hope this helps.susan