While he's always had some hazy notions of what to expect when dying (and proceeded to miss them by a mile), he's never bothered to consider resurrection. Lacking any preconceived ideas, he finds the experience strange and unsettling, and not only due to what he himself goes through.
The return comes and goes quickly: one moment, he's in agony and his grip on consciousness is slipping and every light in his world winks out; the next, he's being dragged relentlessly out and up through a morass of memory and thought and emotion and pain, and startles awake on a hospital bed.
He's drugged to the gills; the sedation and the reality of being alive sit on him like a lead weight, clogging up his thoughts. McCoy looks satisfied with his results, claiming Jim was only a 'little' dead. He seems exasperated, too, maybe because if Jim Kirk can have his devil-may-care cake and eat it too, what's to stop him (or God forbid, anyone else) from doing even crazier things? (Everything that follows for the next three months, it turns out, is quite effective at making Jim think twice about partaking of that cake anymore.)
Spock is unreadable. That's not new, but the mask of stoicism is deliberate and forced, and that is new. Jim's fragmented memories of the end aren't very clear, yet he's sure there's explanations to be had in them if he bothers to look closely. He decides he will at some point, but right now being awake is a pretty major task all on its own, and McCoy clearly has no intentions of letting him stop at 'being alive'.
The last thing Jim expects of resurrection is for it to involve forced walking around the room with Spock as a make-shift crutch. McCoy wastes no time, though; Kirk is back in the waking world for only a few hours before the doctor has him on his feet. "Your muscles and nerves are brand new. It's like Khan's blood regrew everything," McCoy explains as Jim takes some very hesitant steps. It's not just his muscles that feel new; everything from his eyes to his feet is wobbly and untested and unreliable in the worst ways. As Spock guides him in a circuit of the bed, McCoy talks on. "They're really pliable. You need to get them strengthened back up while they're fresh. We'll have to work on your motor coordination, too. Get new muscle memory built in. And until your bone marrow's back, I've got you on shots for a temporary immune system. I've gotta warn you--they're pretty awful. But not as awful as dying of intergalactic flu." McCoy isn't exaggerating; the shots are teeth-grittingly painful and almost always make him nauseated and dizzy for several minutes after they're administered.
Another thing he doesn't expect are the black outs. McCoy does, though, and reassures Jim they won't get worse and will stop in short order. He's coping with nerve regrowth, and the rerouting is complicated by how quickly Khan's blood has laid down fresh tissue. His brain has some catching up to do.
If he expects these episodes or not, Spock seems unperturbed by them. For his part, Jim is relieved when they stop happening a month later, because each time the world dissolves under a tidal wave of black and red and orange, his body goes cold, and he tastes the metallic flavor of blood in his mouth (he always checks afterwards and it's always his imagination). Terror grips him like a vise, and for several long seconds he's sure he's imagined it all and these have just been the last wild thoughts of a man dying on the floor of a reactor core containment chamber.
And each time, the roaring in his head recedes and he comes back to himself in a tilting hospital room with Spock or McCoy sitting him back on the bed. They're both unflappable in the face of it (sometimes he thinks Spock's jaw looks set), which is good because Jim has to spend several minutes collecting himself each time.
Later, under the influence of McCoy's amazing painkillers, Jim tells Spock that there's no such thing as dying 'a little', and definitely not under those kinds of circumstances; it's horrible no matter how you slice it.
"In that case, can I suggest you not try it again, captain," Spock says. He sounds so serious, Jim wonders if it's the sedatives messing with his hearing. He laughs, trying to get enough words together to assure Spock he thinks that's a fantastic idea, and somewhere in the process falls blissfully asleep. (Much later McCoy reveals that Spock watches over him for that entire first night, taking rest only in brief periods of meditation.)
He forms new expectations, and hopes they won't be so far off the mark.