Well I know we have to wait to see the specialist b4 we know for sure, but after hearing about your son I definately think my daughter's is a PWS too. The one thing I couldnt find anywhere was if a PWS can disappear momentarily when you apply pressure - but seeing as your son's birthmark also does, I think for sure that my daughter also has a PWS. My ped just told me last week she thought it was a hemangioma but my daughter's birthmark is completely flat and has not grown (except a little maybe with her face growing ) but is still flat.
Our specialist also uses that same laser with the "cool" mist. From what I have heard from other Mom;s I have spoken to - it really depends on the ped as to whether they are given a general or not. I spoke to Dr Waner's staff in Arkansas and they said they WOULD give my daughter a general (even though her PWS is dimesized and on her forehead). I have heard from 1 other mom at least that they also give their child a general and wouldnt do it any other way. But Ihave also heard from another Mom who's baby is kept awake and she says it is bad during the procedure but it is very quick and her baby is fine as soon as it is over. Not sure if you have ever been to this site before or not but this message board is also very helpful and many people post pictures of their children's laser surgery results which are very promising.
Would love to hear how it all goes. good luck with everything!