it’s my personal headcanon that he was summoned by Cosmos to fight in her war, sometime after he faded away. but, I know not everyone considers Dissidia canon, and even if they did, I don’t think the events of those games took up the entire two years that he was gone… so, he definitely spent a great deal of time in the Farplane.
when he returns to Spira, he doesn’t remember much of anything about the Farplane, just a gnawing feeling of loneliness. it definitely wasn’t an idyllic afterlife paradise, for him. but I think that has a lot to do with the specific nature of his death. it was his choice to go out that way, yes… but it didn’t make it any less painful for him. it was devastating & undoubtedly a tragedy. in Spira, “unclean” deaths can cause one to be “unsent”, where their physical body perishes, but their spirit still remains with the living. in Tidus’ case, it was something similar, except that he was in the Farplane– there was no other place he could be. when the Fayth were sent by Yuna, he had no means to survive in Spira. as a dream of the Fayth, he can’t exist without them. but though he was “banished” to the realm of the dead, he never quite crossed over.
he lacked closure. he was young and had so much life left to live; he’s missing out on things that he desperately yearned for. he’s not at peace. he’s not angry, though, so his soul doesnt lash out and morph into something destructive… he’s just sad, and not ready to move on. he’s in a bit of a limbo state, between the world of the living & the Farplane.
thankfully, he’s not conscious of what’s going on for most of his time in the afterlife– it’s not like he’s floating around in there, completely aware that he’s just a bundle of dead pyreflies, separated from everything and everyone he loves, ajulwkas. no; it’s more like a really deep slumber? punctuated by rare and sudden periods of consciousness, which happens when something particularly meaningful to him stirs his soul & kinda– shocks him awake. like Yuna falling into the Farplane, or, say, Jecht or Auron finding a way to come pay him a visit in his current state. when that happens, he can think & control the pyreflies that make up his spirit, even enough to create a corporeal form reminiscent of how he looked in life. ( he could actually make himself look like anything, but he’s not really concerned with getting creative about his appearance at that time, ahaha. ) he can communicate with the dead through the Farplane’s lifestream-like energy flow that connects them all… but pyreflies can’t talk. so this is why he’s able to communicate in small, distant ways, with Yuna in X-2, but never speaks directly to her. (like how he guides her out of the Farplane when she is lost there, and… there’s also that weird floating moogle that sends her on a wild goosechase around Luca, to all the places she’d been with Tidus. kinda hard not to think he had something to do with that, haha. )
in a way, his stubborn refusal to accept death did work out in his favor, because if he had come to terms with it, he would have moved on to the Farplane completely, and thus he would have lost those opportunities to reach out to Yuna. and I bet that Tidus’ state also had influence on the Fayth’s decision to begin dreaming him up again. they might have felt bad for him, and Yuna, but they may also have been worried. because more often than not, spirits that linger in this “limbo”-like state for too long ( not alive, but not fully dead, either ) eventually succumb to negative feelings because of the futility of their situation. they frequently turn into fiends, or malovelent spirits. it really would not do to have a hero of Spira become a fiend or a villainous ghost.
if he been at peace and moved on to the Farplane, completely, then maybe his experience of death would have been different– less of a solemn quiet, and more of a contended one, perhaps. or maybe he would have even lived among his lost friends & family, in a dream-like world like you described! hopefully he’ll find out the second time around… but idk– it’s kind of complicated & hard for me to explain what happened to him, because it’s a sort of a abstract idea. death in Spira is really complicated, haha. I’m probably not describing it well at all, but I hope this at least sort of answered your question!