As strange as it sounds, this also happens when some of your drivers are not updated. It could be anything but most probably your graphic card. See this link below. It describes the same problem and he was able to get back the sleep options once he updated his graphic card drivers.
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Check if all your drivers are updated. Even if your operating system tells you they are updated, the might not be. Personally, check with the manufacturer's Sites for all the devices you have.
Cheers.