My advice is to take your insurance documents with you on your trip. That way you have the policy number and contact details of the emergency assistance company to hand should you need help whilst you are away.
If you do need to make a claim, contact your insurer as soon as you can. Remember too that if you need medical treatment while abroad, you should contact the emergency assistance number shown on your policy.
The insurer may require evidence to support your claim, for example, if you cancel your holiday due to ill health, your GP will have to complete a medical form.
If you are hospitalised abroad, the emergency assistance company will need to make contact with your GP to check your medical history. They will need to check this against what you have declared when you purchased your policy.