Mac quits unexpectedly

For the past few days I have been experiencing some difficulties with my MacBook. Every 2-3 days, suddenly my screen goes gray and there's a message (on a black base) saying that I need to restart my computer. It says nothing about why. I can't do anything except restart my computer. It just tells me that I need to restart and how to do it. In 4-5 different languages. No installations were taking place that would require me to restart my computer.

Anyway, when I restart, I get a message saying, "Mac OS quit unexpectedly" and then it asks me if I'd like to send a report to Apple. That's it. It doesn't tell me what's wrong or what had happened, nothing.

This has been happening quite frequently in the last few days, and I am a little worried now. I am new to Mac, and have had this machine for about 2 months. But I've "really" been using it only for the last 4 weeks. The problem has become more persistent in the last 2 weeks.

Is it something I should be really worried about? It always happens so unexpectedly. I am worried someday I'll lose my unsaved work this way. It hasn't happened so far.

Thanks in advance for all your help. Its much appreciated.