It sounds like a HDMI handshake issue (The TV and Sky box are losing connection every so often so have to re establish a link - think of like your mobile /tablet having to reconnect to wifi)
First just try removing and reinserting the HDMI - quick but surprisingly effective.
Second try turning off the Sky box at the mains, wait a minute and turn it back on and let it reboot. (There's a reason why "have you tried turning it on and off" is an IT staple!)
Next try a different input on your TV. (If that works the TV probably has a fault sadly)
The next step would be to get a different HDMI cable.
If none of the above works that would point to a fault with the Sky box and a call to them
