What I find especially hard in transitioning from FL HU SNG's to NL ones is that the style I crushed FL with : raw , fearless aggression, you play like a steamroller, just bet-bet-bet and fish often take you on and make loads of lousy calls, makes you a huge fish in NL .
In NL HU SNGs patience is key-waiting for that one big hand, playing nittier and checking and folding way more. You can fold like 10 SB in a row and get it all back in that single hand.
I knew that from a theoretical point of view, but in practice it was really frustrating ( still sometimes is) to play small ball poker.
If you want to learn about NL HU SNGs, Mersenneary free PDF ebook helped me a lot, and for hyper NL, lottelenya's video pack on husng.com That one is great, but not free.