I think my parakeet is sick? =/?

So it's 2 am here and my brother heard a weird noise down stairs. The noise startled my bird and he started chirping REALLY loudly. I've never heard him chirp like this and i've had him for about 4 years. Also, he's never woken up at night. My brother noticed that he looked really thin. I don;t know if he;s always been like this or if he suddenly became skinnier? Is there something wrong with my bird? He's being really weird.