Wisdom tooth fell out?

A few days ago I noticed that my lower left wisdom tooth was missing.

As a 19-year old my upper-right and lower-left wisdom teeth were fully grown (with my lower-right one started to grow out too). So a few days ago, I noticed that I didn't have a lower-left wisdom tooth anymore. At first it hurt a bit when I touched the hole it left behind (as would be expected with any regular kind of wound). The first time I brushed there where the hole was it started to bleed ever so slightly. The next few times it didn't bleed anymore. Now if I go over it with my tongue it doesn't hurt (it still is a bit sensitive, though).

In my entire life I've had only one small cavity. I must admit that I haven't been to the dentist in 1.5 years, and that I haven't always been brushing my teeth as regular as I should. But this was true when I was younger as well; and even then I only had one minor cavity in a life-time.

Should I be worried about what happened, or thankful it potentially saved me from a large bill?