This has happened twice now, after a period of time that my iMac is in sleep mode. i go to wake it up by pressing any key on the keyboard or pressing the magic mouse but nothing happens and i have to physically press the power button once on the imac itself to wake it up from sleep at which point it wakes up right away, why is this happening and how do i fix it? It doesn't happen all the time but it happened twice now during the one week period of me owning this iMac.
The iMac's sleep settings are as seen in the screenshot attached
The iMac's sleep settings are as seen in the screenshot attached