Reid had PTSD after all he went through, he had nightmares that is when he slept and didn't eat that much.
He went back to work and the team greeted hom back with happy, smiling faces. He felt like he was home and when he was with them ge felt like he didn't have to worry.
He told the team how he felt and they helped him through his PTSD. He felt better and was happy to be back at work. Reid felt happier than ever, and he got to work with no worries.