Falling asleep without maintaining awareness

[Traumerei]

So, last night I was counting down from 100, trying to reach SP. I eventually became so tired and relaxed that I would momentarily drift off around 90, then restart my count at 100. This repeated several times until I drifted off until my WBTB alarm six hours later went off. After staying awake for about ten minutes, I tried getting into SP, but lost awareness and consciousness quickly. What should have I done when I was on the verge of falling asleep the first time? Should I increase my WBTB time, and what methods should I use to stay aware? I'd highly appreciate any help on this. (I do realize that WILDs are much more difficult without any prior sleep, however I figure that it'd be best to have two attempts per night.)