Side effect of medication or something serious?

30m 100kgs Hi so I started methadone about 2 weeks ago after suboxone gave me a severe reaction, I am on this medication through a drug program (addiction to opiates) However I have noticed general nausea which I expected. I find that l'm having bouts of vertigo regularly throughout the day which can throw me off balance (I don't fall) I have also noticed my vision shaking at night when I'm really tired, is it safe to say this is side effects of methadone or could it be something more serious like a brain tumor? (I have severe health anxiety)