How To Cure Swollen Ankle?

Hi, I have swollen ankle for no reason. It swell up in just few seconds. This is the second time that it has happened now. The first time I woke up in the morning and found that the ankle was swollen. I did not injure. It feels like it as if it is twisted. There was a bruising around the ankle a few days later. Now it has come back after 3 weeks of the first occurrence. This time I was awake and notice the selling to come up within seconds - I was not doing any exercise.