T520 Extremely slow after a prolonged usage

Specs of my T520 are the following:
i5-2520m
8gb ram
500gb 7200 rpm hdd
integrated graphics card.

I've owned the system for just over a month now, and I am VERY disappointed with how the computer performs after a prolonged usage.
I like to have the computer turned on for most of the day, leaving it idle when I'm not doing anything, and for a quick access, I put the computer to sleep instead of turning it off. However, the system with the spec above proves to be incompetent to handle such "stress."

After a day or two of light usage, just internet surfing, watching videos, listening to music, and etc, the computer slows down without failure. Programs load up with a delay, becomes progressively worse over time. Sometimes, it takes too long that I think that I did not run the program (by accidentally not clicking it or something), but when I look under the "Processes" tab of task manager, the program is running and is in the process of making its way through the traffic. Just now, I turned on the Power Manager by clicking on the battery on the bottom of the screen, and nothing happened for exactly 2 minutes. NO EXAGGERATION. It took 2 minutes alone to have the startup shown, and another 3 minutes until the actual Power Manager program showed up. Also, when watching videos, they skip and lag MASSIVELY to a point the sound becomes distorted, and picture changes every 5 seconds or so.

This is very frustrating. I maxed out to High Performance in the Power Manager, and have plenty of RAM available; usually, the physical memory usage loiters around 60%. I also ran a test on the hard drive, which showed no problem. I don't understand how a computer configured as such cannot withstand a prolonged usage. I tried shutting every program off to see if that is the cause, but the performance still lagged to a same degree. The problem does not go away until I either log off, restart, or shut down the computer.

What might be the cause behind the sluggish speed? This is EXTREMELY disappointing. Please help me getting rid of this problem!

By the way, the computer works as it should when it's just turned on. It starts to slow down ONLY after a period of time.

 

This is quite embarrassing but since I can't delete the post, I should update instead. What the post says is true, but I just learned that after Speccy Piriform is turned off, the computer works fine. I never cared to turn it off since it does not eat up much ram, and I want to monitor the temperature at all times. But the culprit was that one program, amazingly.

Does anybody know why Speccy Prifiorm impacts the performance so greatly?

 

possible memory leaks

 

Boot into the Rescue and Recovery via F11 and run the PC Doctor Diagnostics and see if you have failing hardware.

 

My T520 has a nasty habit of locking up after resuming from hibernation. Google Chrome becomes unstable and DWM consumes some ridiculously high number. Any solutions?

 

Some Schedule Task you have to disable such as "Lenovo-Windows Experience Improvement Program".....this will run at back stage after most sleep/hibernate, also some service like "Windows Defender" will run update after resume.

All those can be simply solved by upgrade to SSD, the problem is cause by the speed limit of Mechanical Hard Drive. Check how busy your hard drive is right after resume, you will get shock.