Acid + nitrous for me is
the combination that makes the most impossible things seem to happen.
In the past I've had the same elusive feelings of chasing a ghost with nitrous, following a thought train that is extremely unilateral. When I finally reach my goal and think I've discovered a couple ultimate answers, they suddenly vanish into thin air and I realize I've arrived at the same point I started from, letting me come down very quickly.
Somehow in the course of time I've lost the chasing like my mind knows it's no use anyway to delude itself

so now N2O does very little for me if I take it sober. Although since my cartload ran out I haven't done it, so my mental tolerance may have left me by now.
Taking acid with it has amazed me a coupla time, and the cool thing is that all normal rules don't seem to apply anymore - making insane things seem to happen, like:
Once I saw a friend of mine doing everything in reverse for as long as the gas was working, I could see it in 360 degrees and it completely freaked me out.
Another time I had the power to interrupt a narrator on TV, just with a simple though popping into my head. He didn't seem to care though :D
I also remember going to a party at some guys house with many strangers, all doing insane amounts of drugs. I took a bunch of acid in the train there. Once arrived I became utterly paranoid and had never tripped as hard. Add some tokes and balloons and I had myself a crazy little dream:
I visualized something like a cartoony cuckoo's clock, feeling it symbolized the moment I thought I had lost it forever. Then it dawned upon me that a caricature version of a police officer busted me in the middle of a street, saying things like "well well what do we have here, wheres your ID little man?" in the most fucked up way I've ever heard 8(
Meanwhile a lot of people at the party were getting concerned for my state, I stuck around for a while feeling awkward and tripping intensely but eventually had to leave early because it was too much or quite enough.
I recognize another thing that was mentioned, namely the occurance of a baffling crazy coincedence.
One time I took the combo I visualized myself als a completely perfect mammal, only it sorta looked like a bunny with a carrot, radiating like all the way. I suddenly felt I was in the prime of my life, feeling strong lifeforce and wanting to masturbate to celebrate my youth. I stood up and threw my roomdoor wide open, only to immediately stuble upon an Antilian guy ironing. This triggered me to snap out of my headtrip and yell 'WHAT THE FUCK???!', what am I doing here almost unzipping my pants in front of an Antilian guy?
Then I had a really bad experience with the combination, my complete body went stiff and rigor and I began laughing so fast, it became a spasm, tensing my body like a surf board. My lungs felt like they got massively damaged because of the pressure that built up. Also I got the feeling of getting a computer-like error message in my head. Like there was a short and I could smell sindering coals. My body communicated to me: "Dude, weak!", and I thought I felt my lifeforce dropping a few levels, bringing me closer to a shutdown or even death. I spectated biochemical processes happening in my body like it was 'fantastic voyage' or something. Later that night i insufflated a little 2C-B with MDMA, and the whippets following were carefree and amazingly visual.
However, the times I tried the combination after that - even after I've almost come down from the acid yielded hypertensive issues like there was a bad association to the bad trip from earlier.
Right now I'm not sure if I will ever overcome this flashback-thingy or if the combination is ruined forever.
All in all, strangest times of my life!