macbook air sleep/wake problem after dual boot I installed ubuntu on macbook air 6,2 (Early 2014 model) using these instructions

https://help.ubuntu.com/community/MacBookAir6-2/Trusty

Now whenever I put my mac on sleep (closing the lid) while using os x, the screen doesn't turn on on wake up. So I have to force it to shut down by holding power key and turn it on again.

What should I do?
This happens to my MacBook Pro also, 98% of the time I get it to work by turning up and down the brightness, even if you turned it off when it was bright. I assume this just gives a prompt to the OS that it is needed again, and should stop sleeping. otherwise, just click a couple times and wait.