Hey there, Skullexx.
In order to find out what might be causing the issue, you should do some testing. First I'd suggest that you backup your data just to be on the safe side. After that go ahead and try the drive with a different SATA port and cables, to see if the same thing happens again. If you haven't installed the SSD dashboard already, please do and let me know if there's anything out of the ordinary when you check the drive's health. Here's where to download it from:
WD SSD Dashboard.
As for the sleep mode, it's up to personal preference I guess. I don't use sleep mode, but I've set my monitor to turn off if the computer's not used for 30 minutes.
Hope that helps. Please let me know how it goes.
Boogieman_WD