I came home from school today to find that one of my zebra danios had buried his entire body into to gravel at the bottom of my tank (My tank has pretty large gravel). Luckily, i could see him, since he had buried himself right against the front. I thought for sure he was dead, but as i moved the gravel away, he swam out. He is swimming around a little bit, but it definitely seems like he is banged up. His spine seems to be bent a little, what can i do for him, and why did he do this?