Has anybody else's EVO rebooted by itself lately?

[gramkn]

Ok, The first time I wasn't too worried. I was browsing the web and my phone just blacked out, stayed off for 30 seconds or so, then started back up by itself. Then the htc evo screen came on and stayed on for longer than usual ( maybe 30 secs.) Then the 4g screen came on and did the same thing. After that, the phone came on as if I had powered off completely.
Well it just did the same thing again. Except this time the htc evo screen and 4g screen stayed on even longer( at least a minute for each.) This time I was reading an email.
My phone is not rooted, I have not accepted any updates, as I intend to root once I've figured out exactly what I want, so I have the original 1.35 software. Sorry to be so long-winded, just wondering if anybody else has experienced this or knows what might be happening. THANKS!!