Someone else may come in here with a better explanation, but my understanding runs something like this:
Physical memory dumps usually involve something using entirely too much RAM when they shouldn't be. The dump takes place to free up memory so that the system could keep running. A few things can cause this, few of them good.
If it's happened twice in a day, it probably means that some piece of hardware it about to go (or already has). Safe bet would be that a memory stick (or part of one) has gone bad. Since the computer expects to be able to use that, it's discovery that it doesn't have all the memory that it thought it did traumatizes the poor thing.
Think of how you'd feel if you discovered that your basement disappeared, right after you bought a bunch of stuff that needed to be stored in there. Your reaction might be to react by just throwing stuff away that you thought was no good and just taking up space. The downside would be that you might accidentally throw away something you need.
The good news is that a RAM dump is not permanently removing information; it's just removing it for the session until necessary. Still, dumps often require restarts because something necessary disappeared. It's not really a great analogy, but I think it helps explain the idea.
You might want to do a check on the RAM or the HDD to see what the problem is. There is also a possibility that it's from a program that isn't bright enough to only use the amount of RAM that's there.