Bit of a long one...
I have spent my career working with heavy drinkers and alcoholics, and in my opinion, Mark had been drinking before last night's "Past the Peak" vlog.
Notice how his skin colour keeps going redder then back to normal and he gets an intermittent light sweat on his forehead?
Alcohol causes vasodilation, or widening of the blood vessels in the skin, which can increase the temperature of the skin. In response, the brain signals the sweat glands to cool down the body, and the perspiration begins.
Alcohol changes the way you think and feel, and therefore influences how you act.
His tone of voice was intermittently louder than normal and his behaviour towards his wife oversteps the mark when he pokes and flicks her. He was, and often is, erratic for no reason. All classic behaviours of a secret drinker who thinks there is no evidence of their drinking. The non verbal evidence is always there.
As the alcohol ravages their body, secret drinkers suffer from skin problems and their overall appearance may suffer. Paying less attention to physical hygiene can be signs someone has a problem with drinking. These are just some of the physical effects I believe Mark shows in response to his secret drinking.
He also drank lots of water throughout the vlog which I believe was to dissipate the alcohol smell and to rehydrate. He's out of breath just going to the kitchen for more water which is uncharacteristic for someone who is fit but not for someone who is drinking.
I'd go so far as to say he's been drinking throughout the lock down. His erratic behaviour has definitely deteriorated online throughout lock down. There is no comparison to the vlogs of old and vlogs of new with regards to his behaviour.
Also Mark stays up late, drinkers often stay up late to drink in peace. Many will stay awake after everyone else has gone to bed. They can drink on their own without anyone monitoring the amount of alcohol being consumed. They feel more free when no one else is there to judge them.
If Mark is relapsing, he needs to get help asap. I believe the evidence is all there for everyone to see. His wife repeatedly keeps calling him annoying, In my humble opinion I would say his behaviour is classic relapsing behaviour.