I have a 3 to 4 year old Sylvania TV that recently started acting up. Once in a while, the picture bows in on the sides of the screen. It lasts only for a few seconds up to a minute and then goes back to normal. It takes an hourglass sort of shape when it does this. Any ideas? I'd hate to have to buy a new one already since it's not that old but I understand electronics aren't really built to last much anymore. :(

Well your first assumption is wrong.

Secondly, I'd suggest that you get an estimate on time and materials for the repairs before the autopsy. It could be as simple as as a cold or burnt solder point, or much more intricate.

If comfortable, and aware of the High Voltage present. Take an insulated tool and tap around circuit board, and with a mirror, watch for an effect. Also there are little heat guns, and freeze sprays that when applied to different suspect components may reveal a thermal intermittent.

Yeah, I should have mentioned the Picture Tube will hold a charge, and can be discharged by taking the plug, which is not plugged in , with back off, by placying a screwdriver between the 2 prongs and twisting cord to make contact with both prongs and sliding under High Voltage line under suction cup on top of picture tube.
This is when working on board, with power off.
Many problems you can see.
Look for dark places on board.

Sounds more like horizontal output or deflection yoke on older TV -- causes hour glass effect