Windows will not update while in sleep mode, since your system is effectively turned off, so that is not the issue.
Normally when you system is in sleep mode for a while, it eventually goes into hibernation (writes the data from memory to the hard drive) and shuts off. This is to preserve the battery, and to prevent data loss should the battery die.
The data is written to a hidden file on the root of the C:\ drive called hiberfil.sys, which is usually pretty large, about 6GB or so, and sometimes that file gets corrupted and cannot be read when you try to resume, thus the laptop reboots since it has no saved state from which to resume.
To fix that problem, you need to disable hibernation to delete the existing hiberfil.sys file, and then re-enable hibernation to create a new hiberfil.sys file, which can be done by following the steps below..
Disable/re-enable hibernation
Right Click on Start and select Command Prompt (Admin)
In the Command Prompt (Admin) window, type: powercfg.exe /h off
It will take a minute or so for the command prompt to return as it deletes the existing hiberfil.sys file
Once the prompt returns, type: powercfg.exe /h on
The prompt should almost immediately return, and the new hiberfil.sys file has been created.
Close the Command Prompt (Admin) window
Hope that helps.
