I am newly sharing my apartment with my dog. Let me explain. I bought a house in 2003 that had a large back yard, which I paid $3000 to fence with a privacy fence, and then I paid a few thousand more dollars to put a dog door through the back of the house. This is a free shelter mutt, remember. Then I got married, and we moved to a bigger house, which again required the fence/dog door combo. Then I got divorced, and friend (now boyfriend) offered to incorporate giant dog into his household, which had recently lost a dog, had an existing dog that liked to roughhouse, and had a dog door and fence. I thought my dog would be happier there. Who knows how dogs feel, but through a variety of circumstances he's now come to live in my small apartment with me and two cats (who ignore him totally).
The dog has picked up the habit of sleeping on the bed, so to sleep I have to contort myself around a large dog and two cats. I am not able to physically move the dog, and everyone knows it is a bad idea to move sleeping cats. He is also accustomed to not only living with dayshift-oriented humans, but also in houses, generally with free access to yards.
Apartments have strange noises, and he has dual views of other dogs being walked (bedroom window at dog height on one end; sliding glass doors on other end). He spends most of his waking hours either growling sotto voce at other creatures or staring at the ceiling wondering about the anvil-throwing neighbors. He is also clearly baffled at being walked and fed breakfast at 4am before I go to bed and at my sleeping all day. Probably he is just annoyed at having to share the bed all day. I don't know. Tonight is the first shift I'll be leaving him before a full 12 hours. He's old and not given to destruction, and he'll likely snooze the whole time, but I worry he will despair and/or bark incessantly. If he tolerates the whole "mom's gone for 12 hours for nights and nights in a row" thing, I'll be officially pleasantly surprised at how well a large dog can fit into apartment living. I have missed having him with me.