Question about sleep mode

[gman901]

I have been enjoying my MBA Rev C for a while now. Tonight, the weirdest thing happened after I fully charged my Air and took it upstairs to work. When I closed the lid and then opened it up when I got back upstairs, the Air would not come out of sleep. The blinking light indicating sleep was not blinking. It looked as though it may have powered off completely on its own. I tried pressing the power button, but nothing happened. I then shut the lid and the light in front came on, but when I opened the lid, the light went out again and the unit never powered up. I waited a few minutes and held the power button down for about 15 seconds, and the Air powered up again. The unit was not hot and the only applications I had up was Mail and Safari when it went into sleep mode. Should I be worried that this could be a sign of future problems or is this a normal issue?