BREATH!!
Waking up from twitching could simply be sleep starts otherwise called nocturnal hypnagogic jerks, night starts, sleep jerks, sleep myoclonus and if you consider your highly anxious state of late and the research that suggests that sleep deprivation, stress or anxiety can increase the chances of twitching in your sleep, you really need to focus on deescalating your anxiety level!
I know your very worried about your dr's appointment but you need to focus on calming your self down when your panicking and remember what your oncologist already told you.....please keep in mind with your preexisting medical history 'IF' this isn't your health anxiety knocking you about after what recently happened in your family, this is highly likely in part going to be the residual effects of the cancer treatments you've had, which are known to cause involuntary muscle movements, sensory and other nerve related issues etc etc and your health anxiety is making you read more into whats going on and has you jumping to worst case situations.....
Breath.......JJ