I had this issue too with non-waking up from sleep. Somehow the problem dissapeared after I upgraded the HDD to SSD. Now everything is working fine. Nonethel

I had this issue too with non-waking up from sleep. Somehow the problem dissapeared after I upgraded the HDD to SSD. Now everything is working fine. Nonetheless, I'm still on Mavericks, no Yosemite upgrade yet. Just a potential solution to your sleep problem.