I have a macbook pro Retina, Mid 2012. I primarily use two wifi connections. One at home and at work I use my own hotspot (Virgin Moble
Overdrive Pro™ 3G/4G Mobile Hotspot by Sierra Wireless. Recently at both locations I have been losing my wireless connection and I've also noticed that the wireless connection does not automatically connect sometimes.
To fix it sometimes I just click on the wireless connection again. Sometimes that doesn't work and I have to turn wifi off, then on and that fixes it.
It happens much more often with the hotspot than at home.