"Okay, I don't mean to spoil the moment, but this isn't working."
"Hm? What's the matter, sunshine?"
Celestia glances up at you without moving her head. The two of you are resting peacefully in your large, fancy bed. It's about eleven at night, and you only just got settled in. Your lovely wife is held tightly in your embrace, her face affectionately buried in your neck and her wings wrapped around your whole body. Being the ex-princess of the sun, she runs a little warm, and the result is an all-around cozy experience.
...Well, except for one teensy tiny issue.
"Tia, your horn is digging into my cheek."
"Oh! I'm sorry, I'll just-" She attempts to move her head to a more comfortable position, but all she succeeds in doing is jamming her horn even farther into your face. "Ah!" She quickly tries going the other way, but considering there's a mattress on that side of her, that doesn't really seem to be an option. "Eh, how should I do this?"
"Maybe you could pull your head backwards a little bit? Here."
You loosen your grip on your alicorn wife and she shuffles a few inches backwards. That seems to do the trick, as her big dumb horn is now right in front of your face rather than digging into it. It's still a bit odd, but a whole lot less uncomfortable.
"Hmph. Your neck is so comfy though." Her voice is a whine, a tone she uses pretty much exclusively around you and never in a serious manner.
"Sorry, but your big dumb horn isn't. I'd never get to sleep with that thing nearly impaling me all night long."
Even though it's dark, you can tell that she's pouting.
"Fine, I guess. Goodnight, sunshine."
"'Night, Tia."
Without another word you fall back asleep, still embracing your wife, just... less tightly.
"Okay, okay, this isn't working either."
"H-hmm?"
You wake Celestia up as you yourself are also awoken to the feeling of her horn once again digging into your cheek. You glance down at your wife to find that she has somehow buried her face back into your neck.
"Did you do that in your sleep, or are you messing with me on purpose?"
"S-Sunshine... go back to bed." Tia's voice is groggy and tired. She has never really been the type to take waking up all that well, particularly after retiring. Apparently having to wake up before dawn to raise the sun every day for over a thousand years tends to build up resentment in a mare. Who knew?
"I can't with your big dumb horn sticking into me again."
"Uuuuugh, sunshiiiiiiiiine!" She's whining again.
"I'm sorry, okay? But I need to sleep too!"
"I can't help how big my horn is!"
"Can't we just spoon like we normally do?"
"Sunshine. My beloved." She looks straight at you with her tired, unfocused magenta eyes. "For over a thousand years, I have been one of the most powerful and well-respected creatures alive. Everypony in Equestria reveres me. I am magically stronger than almost anycreature. I am physically larger than anypony I know of. It's a miracle that I fell in love with someone taller than me. Now that I'm retired, and we're in private, and you're capable of doing so, I want to be held, darn it! I'm tired of always being the one in charge of everything."
"...I-I didn't know you felt that way, Tia."
"Then can you just let it slide? Please?"
You contemplate for a moment. You couldn't let it slide if you wanted to, unless you're willing to get literally no sleep tonight. And yet, just look at her! Look at those big, beautiful, pleading eyes of hers!
"Are you sure there isn't anything you can do about your horn?"
"Like what, darling?"
"I don't know..." You continue to think to yourself in the dark room as your exhausted wife looks to you for a potential answer. "A few years ago, weren't you able to shapeshift into a pegasus?"
"I was, but that was with the help of an enchantment. That thing has long since been destroyed."
"Are you sure there isn't some other way to do that again? Temporarily, I mean?" Celestia closes her eyes and goes quiet, apparently considering your words. "After all, horn aside, you'd be a whole lot smaller. I could hold you tight easier."
"...I suppose I might be capable of transforming myself for a few hours." She looks back at you, a conflicted expression on her face. "Though I'll admit, I'm not exactly keen on going back into that form."
"If you don't want to, I won't force it. It's just a suggestion."
After a few quiet seconds, Celestia lets out a deep breath, apparently having come to a decision. Her horn begins to glow gently, and that glow slowly makes its way across her entire body. Eventually, her whole being is enveloped in that dim light, and there is a magical sound in the air as her body begins to morph and shrink. After a few more seconds, the glow suddenly stops. Where once there was Celestia, now there is a small pegasus mare. Her wings are large, and her braided blonde mane with a blue tuft actually compliments her still-magenta eyes extremely well. "Golden Feather" looks you dead in the eyes, and despite the complete restructuring of her face, you know from that gaze alone that it's still your beloved wife.
"Well? How do I look?"
"Cute. A different kind of cute, but cute."
"Now, then. I did this for one reason, and one reason alone." Without hesitation, Tia throws herself back into your chest, eagerly nuzzling into your neck once more. Unlike last time, there is no big dumb horn to nearly impale you. Though you will admit, you kind of miss having a wife whose legs reach farther than your waist. More cushion for the pushin', or whatever. "Hold me."
With a chuckle, you wrap your arms around your now regular-mare-sized wife. You cheekily squeeze her a bit tighter than you normally would (or could), and you ruffle a bit of her fur in the process. She coos and wraps her legs around you in response, apparently loving the feeling. You give her a quick peck on her big-dumb-horn-less forehead before getting your own head comfortable on the pillow beneath you. She's less warm, but in its own way, this is also quite a cozy way to sleep.
"Goodnight, Tia."
"Goodnight, sunshine."
She ended up shapeshifting back in the middle of the night. You chose to just let her have that one, causing her to eventually wake up a very happy (and cuddly) mare... even if you were exhausted all day afterwards.