One of my high school teachers described me as "taking awhile to warm up."
That's because I started off being quiet and they came across as being outgoing later in the year. Or so my teacher thought.
Looking back on it, I wonder, perhaps she had observed me in a depressed mood and then in a manic mood?
Mania isn't easily recognized. I talked to someone who was manic once (her speech was rapid and she quickly switched from one thought to the next and it didn't make much sense), but there are other shades of mania that seem to present themselves as personality (hyper, outgoing) perhaps accompanied with risky behavior. Since society often equates adolescence with risky behavior, people don't see it as mania.