The amnesia can be trouble to some degree to most everyone including those with florid accounts. The way I go about retaining as much in memory as possible is that while you're there, if you see something special/important/significant that you'd like to keep in memory, you better start pooling all your cognitive resources to
(A): label what you're seeing (hard to remember something without a label) and
(B): start paying attention to detail and focus.
Even if what you're looking at defies all proper labels, come up with a poor one. Come up with anything. It may only poorly resemble a parrot, but if you label it as a parrot anyway, now you have a tag to retrieve your file (a subject for recall). The thing is that you don't really remember half as great as you think you do in normal every-day consciousness. The benefit is that you're surrounded by mostly familiar things which your brain can tack labels on for future recall. In hyperspace, the objects of reference are quite unfamiliar, and even as one builds familiarity with these things through repeated voyages, you still don't usually have the luxury of a parent/teacher figure in hyperspace that is going to tell you what these things are called.
Also, imagine going to see a sci-fi movie. When you leave the theater, you try and recall as much detail as you can from one of the scenes. You may come up with a very rough oversimplification of what you saw, and you'll likely only remember a handful of the macro details of an intricately composed scene, and should someone ask you what happened in that scene (which we'll assume has no dialogue), I'd bet you'd find yourself a bit hard pressed to create an accurate verbal representation of exactly what it is you saw. That's human memory and language for you. The other problem with DMT of course is that you can't turn to the guy sitting next to you and say, "hey, you remember that really weird big green glob thing?" That would make it so much easier wouldn't it?
Last tip I have for trying to remember what's happened in hyperspace is listening to music. As I've said, one of the most difficult part of the recall is not having a label or description under which to recall, but if you're listening to music, the music starts to do the job for you. You see, let's imagine you're looking at that parrot-looking thing as mentioned above, and you have no idea what to call it, or even what it resembles. If you're listening to music while you see the "parrot" and then when you're out of hyperspace, you go back and listen to that same music, the part in the music when you were looking at the parrot the first time, could very well start triggering memories of it later. Like "oh yeah, when I heard that, I was seeing..." In this case, it's almost like the music is your recall label.
"Science without religion is lame. Religion without science is blind" - Albert Einstein
"The Mighty One appears, the horizon shines. Atum appears on the smell of his censing, the Sunshine- god has risen in the sky, the Mansion of the pyramidion is in joy and all its inmates are assembled, a voice calls out within the shrine, shouting reverberates around the Netherworld." - Egyptian Book of the Dead
"Man fears time, but time fears the Pyramids" - 9th century Arab proverb