My new Comet Goldfish is Darting and then sitting on bottom

[Alma@fish]

He is by himself for now because I just got him. He is darting around frantically and then staying on the bottom of the tank. Is he just nervous, or is he sick? I don't know! Please help!

 

[Alma@fish]

Plz help! I have no clue!

 

[Natt]

Hi! does your goldfish have any white spots on his body? also what are you tank dimensions and ammonia, nitrite, nitrate levels?