I just don't feel the need to sleep
insomnia is more like you want to sleep, and you're tired, but... can't sleep. think restlessness or
think of it like when you get really ill and feverish and keep waking up in the middle of the night, except all the time. i was a diagnosed insomniac way back when at the start of high school due to stress (long distance relationships.. ew), but i'm all better now. worst time of my life. but don't worry, insomnia isn't (usually) permanent, and you'll probably be back to normal within a couple of weeks.
although, i know what you're talking about, too. you just end up staying up super late and never really finding the need to sleep until dawn? that could actually be stress related too, i used to do that through summer. it was awful and i felt like i missed half of my summer.
school came around and forced me to wake up early, so i started falling asleep earlier again... lol