My son just turned 20 months, and he started having complete melt-downs! What do I do?

He has always been a little temperamental, but he recently started having melt-downs, where he wants me or his father to hold him while he screams and cries and points at nothing in particular. When I try to figure out what he is pointing at, he starts pointing at something else altogether, so obviously even he really doesn't know what he wants. He will carry on for 20-30 minutes without stopping, no matter if I ignore him or try to appease him. The only thing that makes him stop is putting him in the car and driving for a bit. This has happened probably 5 or 6 times now in the last 2 weeks, and if I don't figure out what is wrong with him I am going to have a meltdown myself.