Asperger's and Medication for Meltdown/Panic Attacks

Hi, my name is Chris and I'm an Asperger's sufferer and the father of a high-functioning Asperger's boy, well , young adult now. My son has been suffering with depression and anxiety, and has been having severe panic attacks. Mix this lot up with Asperger's and he has has severe breakdowns that he, and we, are failing to manage. He has been prescribed Daizepam in the past, amongst other things, and it has been very effective in bringing him out of the irrational, delusional state and allowing us to talk him down. Nothing else has worked with him, including mindfulness, meditation, and the suchlike. Once he's broken down he's virtually unreachable. Unfortunately, his GP has ramped down his Diazepam dosage/prescription to 3 tablets a month (from 7)and is citing addiction. Has anyone else had experience with Diazepam and Asperger's? As it been effective? Any GP reluctance to prescribe?