My face hurts from smiling. My left arm feels as though I have been lifting weights.
My neck aches from supporting so much furniture on my head: a wig, then a crown, then a hat.
Quite a big hat, actually, and dingly-dangly earrings. I don't think I've ever been more exhausted.
I have just spent the day as Her Majesty the Queen to find out just what goes into looking and behaving immaculately at all times and how it feels to be the most famous woman in the world.
I had a crack team to help me with my transformation a stylist, make-up artist and wig expert before I stepped out onto the streets to meet my subjects, and the real work began.
Who knew so much effort was required to keep a hat on one's head? And those white gloves?
How has Her Majesty coped for 80-plus years with not being able to scratch her nose or in my case tap out a text? And don't get me started on the smiling and waving.
But most importantly, there's the poise, the manners and living under constant scrutiny.
There's an awful lot that goes into being a monarch, I can tell you.
Arriving at Buckingham Palace, I admit I was nervous about being dressed as the Queen so close to home.
Such irreverent behaviour would have earned me a spell in the Tower a few centuries back, but the attendant policemen, although shifting uneasily on their feet, did not approach.
But this is 2012 and the tourists did. In their droves. The level of mania incited by the sight of someone vaguely royal in their midst was unsettling: I am videoed, photographed and Tweeted relentlessly.
How odd, to be gawped at and have small children run up and offer me flowers. I bent from the hip, like the Queen, causing my hat to fall on one child, and then had no idea what to do with the darned blooms, which dripped water on my shoes.
What is the etiquette when one's hat is whipped away by a gust of wind? The Queen must have sourced some good, long hat pins during her 60 years on the throne.
She has also learned to behave as if she was carved from stone. Unseemly reactions to unexpected events can never be becoming for a monarch.
I was amazed when I found out how long it takes to achieve the Queen's "look". Fai, the make-up artist, Desmond, a wizard with wigs, and stylist Nicole work for hours on my make-over.
Although the Queen's look is simple, it is very difficult to achieve and almost impossible for a mere commoner to sustain.
First, she does not wear much make-up: just foundation, powder, blusher and a natural pink lipstick.
There is very little adornment on the blue, lively eyes (my lash extensions are summarily removed), merely a frosted pale shadow above. This means that during a long day, she doesn't have to worry about mascara smudges. The once finely-arched brows of her youth are now blurred and sparse. My brows are duly obliterated with powder.
Two deep tramlines from nose to mouth are drawn on by Fai using a purple pencil: these crevasses are the reason the Queen looks dour when not smiling.
I'm given crepey skin around the eyes with an application of latex, but my face is largely left free of prosthetics. What does surprise me while studying pictures of Elizabeth's face (I was named after a Taylor, not a Windsor) is that she has surprisingly few wrinkles: there are the two curious horizontal lines just below her nose, a few crow's feet and a certain pouchiness around the jowls. But that's it remarkable for a woman in her 80s.
At the start of this long day, I put her soft, peaches and cream, very even-toned complexion down to the lack of stress or hardship in her life. Oh, how very wrong could I have been!
Next comes the wig: my own dark mop was pinned up and secured beneath the buttocks of a pair of tights. Then, a curly grey wig was pulled over the top.
The Queen has had her hair styled by Ian Carmichael for 14 years, and her unchanging style springy curls around the nape, a flattering, glittery pale silver halo that never veers towards yellow, or iron or, God forbid, blue made sense: it takes perfectly the addition of a tiara or crown, and is never flattened by a hat. It never blows across her face or gets stuck to her lipstick.
She (and I) never have to touch it or fiddle with it. Perfect!
And then come the clothes! The Queen has a dresser, the trusted and long-serving Angela Kelly, the only "servant" ever to see the Monarch in her Rigby & Peller underwear.
When being fitted by her favourite couturier, Berkshire-born Stewart Parvin, 45, the Queen wears a body stocking that covers her from neck to ankle (she loves being filled in on all the latest celebrity gossip while she is pinned and tucked).
My "dresser", Nicole, puts me into a long, cream vintage gown which she then immediately clutters with the intrusive ceremonial sash and brooches.
Three-quarter Cornelia James gloves are pulled on, with diamond bracelets on top, but rings, curiously, remaining underneath. The formal gowns are always simple and unadorned, given the jewellery (off duty, she wears pearls).
I soon find the gloves hot and cover them in make-up because I keep touching my face and lipstick. I find I can't text (the Queen probably does not feel the need to social network using a BlackBerry).
The handbag becomes insanely heavy, but I'm not allowed to put it down, sling it somewhere or hug it.
I'd studied footage of the way the Queen walks: she never rushes, as people waiting to watch her pass would be offended. As someone who is always rushing, I find it frustratingly difficult to slow to a regal pace.
The level of concentration required has utterly floored me, and I am 30 years her junior.
"The level of concentration required has utterly floored me," said Liz
Watching her arrival in full regalia at Westminster last Wednesday, I can now appreciate the level of yogic poise and almost superhuman gravitas required to carry off the jewels and the ermine without looking foolish, or bursting into giggles.
Here are a few things I must do to be just like her. Never allow my eyes to glaze over. I must listen to what others are saying, and never yawn. I must not shiver in the cold, or cross my legs, or slouch.
Or show my knees. Or be anything other than serene and benign while tourists in crazy outfits take my photograph.
Finally, back in the studio, I pose for a more formal photograph, and as I do so I think of all the formal photographs the Queen must have stood to attention for.
All the sittings for painters. All the displays of traditional dance she has sat through. The processions. The dinners next to men who do not speak English.
Oh, the backache, the boredom! The times she would have so preferred to have curled up indoors, watching Homeland.
I wonder how the Queen has managed to do her job for so long when 10 minutes spent waving out of a taxi window leaves me howling with pain and cramp and cold.
Of course, her life has been stressful: to glide through it as if you are on casters is so much harder than what the rest of us do.
But most of all I pity the Duchess of Cambridge, who has a lifetime ahead of her spent sitting on tiny chairs in primary schools, finding the banal endlessly fascinating.
How wonderful it must be, I'd always thought, to live in a palace. What do the royals actually do for their money?
Quite a lot, I realise. I can't wait to rip the wig from my head, and let my hair down. Literally. I want to roll my eyes, and yawn, and get back to life among the common people.
The Queen is certainly made of sterner stuff than me. Let's hope Kate is, too.