my turkeys started doing that and long story short i lost the entire flock (10 x 12 week olds)
turned out to be cocci (even though theyd been on so called medicated feed since 1 week old)
keep an eye on his stools, if they begin turning yellow it could mean cocci or blackhead disease.
could also be something as simple as a lack of vitamins. try some electrolytes in his water, see if he perks up. in any case id quarantine him from the rest while you figure out what it is....that was the mistake i made (not quarantining straight away) and it spread like wild fire through the flock within 3 days.
has he gotten wet at all? young turkeys + getting wet or getting hot = sick poult. humid conditions are perfect for cocci to spread...