I’ve been lurking for a while, reading through the previous thread and finding it helpful.
I have a 15yo DD whose mocks start mid-Jan, although they randomly had one English literature and Maths mock last month with just a week’s notice 
She dropped French at the beginning of this term after much deliberation which has been a huge weight off her shoulders as it was her weakest and most stress-inducing subject. A bullying cover teacher added the final nail to the coffin and we decided enough was enough.
My DD is trying to undertake some form of revision/preparation every day, but in short bursts with plenty of rest. She’s battling some challenging health conditions which have relapsed as a result of the stress and she sat the two mocks dosed up on antibiotics and pain relief as a result.
School are fully aware and I’ve requested considering for extra examination time where possible, plus discretionary study leave as they revoked study leave for all year 11 students two years ago.
We’re supporting her as best we can and she openly welcomes help with revision planning, revision itself and talks freely with us. She’s a very stoical young lady.
Wishing everyone a Merry Christmas and a positive parental examination experience(!)