Hi, ebony321,
Sorry, but I (slightly) disagree with Brava 210 's advice.
An insurance company may penalise you for a medical condition and/or impose conditions on your policy, depending on the condition, its severity and any added risks it incurs. They can refuse to insure you altogether if they consider the risks too great.
Failure to notify them of your condition would almost definitely invalidate your insurance in event of a claim.
Insurance companies talk to one another, but it is always worth shopping around. But do not hide information if they ask for it.
Dependant upon your particular medical condition your G.P. is legally obliged to notify the DVLA.
Also ebony 321, you didn't say which country you reside in, so I have assumed it to be the UK.