When I flush the toilet, everything seems in order. The toilet tank fills to its normal level and the bowl fills with water. After about 5-10 minutes, the water in the tank drops making the toilet inoperable unless I take the top off the tank and push down on the lever to fill the tank again. Then, I can go ahead and flush the toilet. If I stand there and continually flush the toilet, there's not problem. The problem comes after letting the toilet rest for more than 10 minutes or so. It doesn't happen due to any other fixtures being used either. Any suggestions on how to fix this problem or do I need a new toilet? Also, if I need a new toilet, is it hard to install yourself? I'm not plumbing savvy and don't possess the plumbing lingo.

Thanks in advance,

CL