Re: Phone resetting by itself
A few possibilities:
1. Glitchy system update. Samsung has had a run of bad updates lately. How long ago did yours update?
2. Bad battery. Take it out, lay it flat on a table, and see if you can spin it freely. If so, that means it's bulging in the middle, which means it's going bad. Replace it.
3. Screwy SD card. Some have noted improvement in glitches like that by removing the SD.
Let us know if any of these help!