He's channeling his inner Batman. Something in the way...

I believe it was an extra detail showing how Anakin has fallen under the Son’s influence. Ahsoka had similar dark rings around her eyes when the Son corrupted her as well.

Swayed by visions of his dark future, it didn’t take much effort for the Son to convince Anakin that joining him would prevent said visions from coming true. The difference between Anakin in S3E17 and ROTS is Anakin was power hungry and he wasn’t looking to rule the galaxy. He was looking to stop Palpatine from destroying the galaxy and his life. I know that has almost nothing to do with the dark rings around his eyes but I love examining Anakin’s character.

A lack of sleep. Happens to the best of us.

Almost every sith looks like they're sleep deprived

Maybe they are taking the view of the dark side as an addictive narcotic.

They got off their tits on death sticks and spice the night before they landed on Mortis. Explains all sorts.

^Now they need to just go home and rethink their lives.

Anakin does a catering diploma to get himself back on the right track, Ahsoka gets grounded for three weeks and Obi Wan sets off to Ibiza to find Death Sticks guy. Who is really Jesse from Breaking Bad.

^Wait! Jesse was in on it???

What do you think all the pockets and pouches are for? Jesse patterned up. Allow it fam. Or something.