PET scan post treatment showing concerns

My Mum was diagnosed with head and neck cancer last year. She had 2 surgeries & radiotherapy to "mop up" any microscopic cells. There was no spread and having surgery & radiotherapy the doctors seemed positive about the outcome. Even so far as the Dr she saw last week said he didn't have the results of the PET scan but based on his examination of her he was "confident it would be a good result". 

However she's just had a follow up PET scan (3 months post radiotherapy) which has showed some areas of concern that need more investigation. I know it could be a variety of things but my mind goes to the worst. 

We've got to wait 2 weeks until she next sees someone and I feel like I can't cope. I have suffered with extreme anxiety & depression even before my Mum's illness. I'm beyond terrified about what the results could mean. I feel sick, am struggling to eat and can't stop shaking.

My Mum is also struggling to cope & not sleeping. 

Has anyone else had experience of what they thought was a going to be a positive outcome of treatment only to be blindsided by completely unexpected results? I don't know what to do. Talking to my Mum ends up with us both really upset & I'm trying so hard no to show how scared I am.