Sudden Hair Loss

Hi. I'm in my 20's and about 3-4 wks ago, a clump of my hair came out. I don't why. At the time, it left a smooth, red half-dime-sized spot on my scalp. Now, I see only a few strands (maybe 1/8 inch long) sprouting - which is slow considering I get about half an inch of growth per month. However, the smooth area is still very visible. I'm not even sure if the hair follicles are still intact (that is, my hair will grow back) because I don't see the little "dot" things where the hair grows out. My scalp is still red and I noticed last night that the spot is kind of soft and a bit deeper than the other places on my head. I'm wondering if I hit it somewhere, but I don't remember.

So, my questions are:
1) Could a minor bump on the head cause hair loss?
2) Will my hair grow back? (Even in the places where I don't yet see hair follicle dot-things?)
3) If so, how long should it take?