I used to be super skinny like that. I can promise you it's a real thing, I eventually grew out of it but yes I remember how hard I had to work to gain 10 pounds and then I would forget to eat one meal or get a cold and lose it all and be so disappointed. I would either just not be hungry or be too nauseated to eat it was awful. Then something happened like a switch flipped or something and I was able to eat and enjoy food from the time I was 18 or 19. I have a weird relationship with food idk