Yes, permanent sadness is called like this if someone is non stop sad for over 3 weeks...

And Branch has been sad... For 20 YEARS! O_O  ( can you imagine it?... - Some of you reading it probably don't even live That Long yet! )

He was the Only 'Sad Troll' in Troll Village 

- So why noone helped him earlier? ( They probably didn't have Trolls Psychologists there because Other Trolls Were HAPPY - so they wouldn't need that!  😁 )

No wonder that some user compared him to Grinch ( I saw a fanfic 'How Branch Stole Christmas' here )

And Why Was he Like That? :/

- He used to be Happy & Singing like All The Trolls as a kid - but his Traumatic childhood experience changed him for many years: He lost his beloved Grandma because she saved him & didn't let Chef get him when he was singing - so Chef caught HER & he was blaming himself for That. ( Poor Branch, he was a little Kid then - so he didn't have a happy childhood because his next 20 years, so rest of his childhood, all his teen years, & earliest 20-ies were SAD! :(  )

He became a grumpy, pessimistic loner - yes, very much like Grinch. He built an anti Bergen bunker ( it must have taken him a few years ) & locked himself in it - & when he was coming out of it - he was always complaining, telling rude or sarcastic things or Ruining some Trolls celebrations running around & screaming 'The Bergens are Coming!' because he was expecting their attack anytime. 

So his Depression was with Anxiety or Paranoia - to be precise. 

And how is that Possible that he Stayed Sad For So Long although he was Surrounded with Happy, Singing & Dancing Trolls who were trying to cheer him up every once in a while as much as they could? 

- The answer is: That's How Depression works, & you must be willing to fight it & strong enough to get out of it Yourself - cause if you get lost in your sadness & don't accept help Nothing Will Cheer You Up in This World!... - Yes! You must want to change something! - It's You who must Want to Be Happy Again! 

Luckily Branch finally decided that it was time for a good change &: 

- He finally got out of his Bunker, followed Poppy on her Reasue Mission to Bergen Town & saved her life btw ( remember that he first said 'No' when Poppy asked him to go with her? - Seems that he thought about it again & changed his mind - Good for Her, & for Their Kidnapped by Chef Friends - because they managed to save them Together & he started behaving 'Like a Happy Troll' again )

- And it was Him who cheered All the Trolls up when they all lost their colors in that Bergen Pot. He sang them a song with his Beautiful Voice for the First Time since 20 Years! - & they all Were Happy & got their True Colors Back again. - His True Colors came back too

( So now you may ask: 'What? - They've been singing next to him for 20 years & he was still Sad - & suddenly This one 'True Colors' song Made a Miracle & he got Happy Again? :D ... - Yes, because He Wanted it, and he decided to be Happy At Last!  ^_^ 👍 ) 

There was 'too much sadness' Even for Him when All the Other Trolls turned gray - They All Lost Their Hope & Were Sad then - SO He was THE ONLY ONE ABLE TO BRING THEIR HAPPINESS BACK! ... - And He DID ! 😁👍