It's possible to WILD without prior sleep, but it's excruciatingly difficult. First, you'll probably have to relax a ton to get into sleep paralysis, for at least an hour in most cases. If you're very tired, that will help. I've seen HI when I was tired before, without sleep beforehand. Since you're not in REM yet, if you do manage to get to sleep paralysis, you'll either enter a very short dream, or fall unconscious and drift asleep.

For most people, it's easier to just do the WBTB and then WILD. It's not really worth the effort.