Swollen ankles can be because of many reasons but it is also a sign of dangerous disease which you should never ignore.
Oedema is a health issue in which body fluid starts to build up which causes ankles to swell. Other symptoms of this disease include skin discolouration, increase in weight and aching limbs.
When fluids starts leaking from tissues gravity pulls it towards your ankles where it starts to accumulate, this causes the swelling of the ankle and may also cause pain.
If you feel pain and swelling then you should visit your doctor who will prescribe you some medicine and will ask you to gently massage your legs. Usually oedema is treated within 24 hours but if the problem remains unsolved then you should visit specialized clinics and doctors who will start your therapy which will end the swelling.