Hi DizzyLizzy and welcome to the forum.

Being diagnosed with cancer is about the scariest thing imaginable and many of us on here can empathise with how you feel through personal experience! 

Don't hesitate to talk to your GP and get some help with sleeping. I had a similar issue and was put on some anti-anxiety meds whose primary side effect is drowsiness. It was just enough to break the cycle of natural situational anxiety causing lack of sleep which caused more anxiety, which resulted in lack of sleep etc.

Best wishes

Dave