Grace Dent: ​I wonder why the truth about my 2015 doesn't really tally with what appeared on Instagram?

Over the past 12 months I have been constantly joyous, and a linchpin in my social set. My arms were thin and my skin was luminous. I exuded a raffish joie de vivre.

Oh for the days of my teenage diary, daubed in felt tip, heaving with gritty detail (Ping Zhu)

It's the traditional time of year to take stock of one's personal behaviour, survey the past 12 months, and cock an eye towards self-improvement. Clearly, this has limits. If you were a gigantic arse right the way through 2015, you can't start rebuilding your personality from scratch.

Yes, you might, come January, go through the motions of appearing less shallow, showy, stalky, greedy, needy and socially upward-scrabbling, but rest assured, being an arse lurks in the very nub of your soul.

To these people I say, carry on – please. If we didn't have your awfulness to dissect daily on WhatsApp, well, we'd only start eating each other. It would be a sad day for civilisation if all the most awful humans became self-aware. Hell is other people with suddenly locked Instagram accounts.

Of course, to take stock of 2015 you really need a good honest look at what you've been up to. Here my problems begin. If you're like me, then the year passed with terrifying swiftness and one can only account meaningfully for around 17 hours of it. Go on, try. What did you do this year?

I remember sitting behind a laptop a lot. Sometimes in bed. Sometimes on the sofa. Sometimes in the little café over the road that sells Dime-bar cake and where 11 in the morning drifts into 4 in the afternoon, and then I buy groceries for dinner. I definitely repainted the hallway. And I remember locking the house up and going to bed, many many times. Even if all these times now merge into one long, moonlit search for the back-door key, which may or may not be in the dog's bed. The dog definitely stole and ate – or attempted to eat – a lot of things during 2015. Be sure that when I write my memoirs that I'll pepper these ripping real-life anecdotes throughout the text to keep my Amazon feedback bouyant.

Perplexed, I scrolled through my Instagram account for more meat and bones from 2015, and was comforted to see that my life has been marvellous. No changes needed here. Top marks for me. Over the past 12 months I have been constantly joyous, and a linchpin in my social set. My arms were thin and my skin was luminous. I exuded a raffish joie de vivre.

I spent most weekends at hot new, much talked-about places, while still managing to be a dedicated home-maker, stirring a Le Creuset casserole in my kitchen, which has no recurrent ants' nest and no drawers stuffed full of carrier bags and broken travel adapters. Admittedly, I have some doubts about Instagram's reliability as a diary. It looks nothing like my 2015 at all.

There's no record of the time in October I ate scallops while judging a food competition and erupted in hives, spending the next three weeks resembling Jabba the Hutt, my face caked in concealer. Don't worry, this incident will be in the index of my memoirs, appearing under “S” for “scabby face”.

The iCal that syncs my schedule between my phone and my laptop reveals even less about my year. Coded phrases like “Cocobrown-Fran-Albert” denote that at some point in May I was sprayed a rich mahogony shade, before seeing Nick Cave at the Royal Albert Hall. That was, incidentally, one of the greatest gigs of my life – although because I didn't Instagram, tweet, or make a YouTube diary about what I saw and heard, it arguably doesn't count as an experience.

According to iCal I spent too much of 2015 at the mercy of fruitless face-showing meetings and “quick coffees” which achieved little more than a tepid plan for other meetings. I shall gloss over this as it's an unpalatable truth. Also it doesn't account for about 350 evenings and 50 weekends.

Oh for the days of my handwritten teenage diary, daubed in felt-tip, heaving with honest, gritty detail. Pages and pages of piffle. No need to wonder where 1988 went, it was documented with eye-watering clarity. “June 9th – party at Karen's house. Kelly got fingered. I was sick in bush and on Karen's dog. Need to buy bottle of Impulse to say sorry.” Each entry was packed with lovingly vivid minutiae. Not only could I account for every single day in 1988, so could my mother. She'd have that diary from under my bed, filleting it, the second I left the house in a choking cloud of Boots 17 Extra Hold.

In 2016, besides tidying my home using the Mari Koning method, finishing my Booker-worthy novel, and doing squats until my arse is like Khloe Kardashian's, I want to be more alive in each moment. That's real self-improvement. Next year I shall notice what I'm doing. And I'll enjoy myself more. It's later than I think.