This truly sounds like it is most likely an ankle sprain, which involves stretching or tearing the ligaments on the outside of the ankle, known as the lateral ligament complex. There are three ligaments, and depending on the number of ligaents involved and the severity of the tears, sprains are graded 1 -3.
Treatment of Ankle sprains very rarely involves surgery. However, proper treatment, including functional bracing and occasionally PT, is essential to avoid chronic instability. In addition, I would recommend an X-ray to be sure there are no fractures. In the meantime, remember RICE: rest, ice, compression, and elevation.
*I posted the pictures in my album
*(Clarification) Swelling occurred immediately after the injury but the bruising began late last night.