TV was playing with No Antenna connected

This happened a few weeks ago and it's really baffled me since it happened, if anyone could share any insight to this or possible causes It'd be greatly appreciated.

My son was watching telly in our room all morning, he came downstairs around 11am and left the telly on cause I could hear it playing from downstairs.

Around 12pm I go into the bedroom to lie down myself and charge my phone, I noticed that the TV was still playing in the background but I didn't take any notice as I was on my phone... About 10 minutes go by and I notice the TV is losing signal, keeps crackling and picture keeps going on and off. I moved the aerial and it went completely off. I moved the aerial around everywhere and couldn't get any signal, then I looked down and the aerial wasn't even plugged in. My son didn't unplug it because he never does that and I physically saw the TV playing when I came upstairs.

Is there any like strange occurrence that caused the aerial/antenna to get signal and power up?

P.S it's a plug in mains aerial..