Having run the gamut of glitches and grief since doing the High Sierra upgrade ( and subsequent updates) I was at my wits end with respect to the "Sleep-Wake-Fail" & rebooting , which was occurring 2/3 of the time when the iMac was sleeping. I am resigned to simply waiting until next fall when whatever replaces High Sierra comes out, hopefully all the crash reports are going somewhere ( I send them,- per the on screen request, every time ie more than daily,for at least 2 months) and there will be a fix. However what I've found works very well is s to use the 'Power Saving' settings to tell the hard drive to stay awake all the time ie sleep-NEVER, while selecting 'screen sleep' to any realistic value ( I chose 45 min). As a personal preference I use a screen saver ( stock) from 5 min inactive to the screen timeout at 45 min. I've had it set up this way for a month, and the computer is faster than its ever been ie 'better than new'. ( It's a late 2012 model) Browsers open instantly and mouse and keyboard respond 'lightning fast' for any function. I have never had even mild warmth or heard any fan activity indicating that the HD is in any way stressed. While experimenting with this set up I did try a few times to 'manually' select sleep but I still would get no end of issues ( foggy, slow wake ups plus Bluetooth issues, after any sleep over about 2 hrs, plus the sleep wake failure / reboots being constant) . Am I abusing the hard arrive simply by only sleeping the screen? - since the performance has been 110% of what it was in the years even before the High Sierra issues.... I believe that that many office setups do not use sleep modes and the HD's run 24/ 7 with adaptations to save a bit by simply sleeping the screen. I live in the Caribbean so ambient temperatures are relatively warm ( high 70's at night, mid 80's day and the room where the desk and iMac are located doesn't not have AC but as I said, the entire screen-back remain cool to the touch at all times. I had to dig a bit to see if the HD was solid state, but it's not....
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