We spoke to a couple of experts, a mental health charity and someone who spends Christmas on her own every year - and loves it - to find out what tips they would offer someone preparing to be on their own this Christmas Day.
1. It's OK to be angry
If you're really cross about your ruined plans, that's OK. "We are in extraordinary circumstances and I think people have every right to be angry and disappointed and sad," says Helen Russell, journalist and author of the book How to be Sad.
"We have to acknowledge and give space and sit with that sadness," she says. "Suppressing the negative thoughts doesn't work - they come back with a vengeance." She says many people find change difficult, so don't worry if you feel unsettled.
Accepting that this year's festive period will be different is key, she says. She suggests changing the way you look at the day: "You can now rewrite the rules and plan something different." Martha says she treats it as a "decadent" day of self-indulgence and self-care. So do what you like.
And if there are events or traditions that you can't do this Christmas, it may help to think of them as paused rather than cancelled. Mind, the mental health charity, says "postpone them until next year, even if they happen in the summer".
3. Plan, plan, plan
Don't wake up on Christmas Day not knowing what you are going to do. "I have to hold myself back from planning too soon," Martha says. Planning the day out allows her to break it into bit-sized chunks. So plan what you are having for breakfast, set some time aside for reading, or a walk, or an afternoon film, or ringing relatives.
"Make sure you have some nice food in, have some people you know you can video call or just text, and make sure you have some sort of agenda for the day."
Mind also recommends taking some time to make your home feel nicer. "This could be putting up Christmas decorations, or extra photographs." It could be as simple as tidying up. And try to plan something nice to do after Christmas. "Having something to look forward to next year could make a real difference," the charity says.
4. Do what makes you happy
Spend the day doing the things you enjoy. "This could be taking a morning jog, playing video games or doing puzzles," the charity says. Equally it could be having a hot bath with a good book, or a lie-in wearing your favourite pyjamas.
If you haven't got the pressures of travel or fitting in with other people, then you can simply focus on doing what makes you happy. Buy yourself a present or get something you've always wanted. And wrap it up to then unwrap later!
"Do what will make you feel good in terms of sensory things. I like to make sure I have a nice Christmas scented candle in. It is just being kind to yourself and being gentle with yourself," Martha says.
5. Speak to other people
If there are people you'd like to speak to, you could arrange to talk over the phone or via video call. Or you could watch a film together, or do a quiz. British comedian Sarah Millican hosts a Christmas day chat on Twitter each year, which anyone can join, Mind says.
And if you are feeling isolated or down, try getting outside. Sophie Scott, professor of cognitive neuroscience at University College London, says getting outside, even if to only walk around the block, is "one of the best things you can do for your brain and your mood".
Martha agrees. She says cheery cries of "merry Christmas" exchanged with strangers and dog walkers will help.
If you love turkey - and can still get one from your local shop - then do it. If you hate the stuff, buy something else. There are no rules about what you should and shouldn't eat, so get in some food you can look forward to eating.
"Plan to enjoy your favourite food or drink," Mind says. It doesn't even have to be dinner. "It could be a special breakfast or some interesting soft drinks. It could be a good excuse not to eat traditional Christmas food."
"If you want to just have salad for lunch, or eat peanut butter out of the jar for breakfast, then do it," adds Martha.
7. Don't celebrate at all
Of course, you may decide not to mark Christmas at all this year. You could treat it as if it's any other day. "This may feel easier than trying to celebrate alone," Mind says. "It's completely understandable if you feel this way".
If you decide to skip it, the charity says you could let others know your plan. Say you're happy to hear from them on Christmas Day but tell them "they can also support you by treating it like any other day and not mentioning Christmas".
If you are planning to give gifts, exchange them in advance. And the charity advises staying off social media to avoid Christmassy posts, and trying to avoid adverts on TV or online.
"A lot of people get bogged down in thinking they are not going to enjoy it," Martha says. "And that's OK." It's important to realise Christmas Day is only one day - and it will quickly be over, she says.
"It is only 24 hours and it won't last forever. If you are having the worst day ever, you will go to bed that night and when you wake up Christmas Day will be over."