Can Alphonse sleep in FMA/FMA:B? In both Fullmetal Alchemist (2003) and Fullmetal Alchemist: Brotherhood (2009), there are instances of Alphonse Elric saying what he can't wait to do once he gets his body back. He usually states things that only humans/living creatures can do that he cannot, such as eating and smelling. 

Since sleeping is something that only humans/living creatures (i.e. - not a suit of armor) can do, does this mean that Alphonse cannot sleep? Does he just sit there all night on Ed's floor? Is this talked about/approached differently in the two shows?
To simply answer your question. No he cannot sleep. I found the below referenced in the fma wikia here.


  Additionally, his armor body has several combat advantages including - strengthened offense and defense, imperviability to bullets, inexhaustible stamina, invulnerability against extreme temperatures and an exemption from needing to breathe, eat or sleep. 


Although, it only states that there is no need for him to sleep. I am 100% sure that in the anime, Alphonse explains Elric about the horror of not able to sleep and the pain he suffers in solitude. It is a very sad situation that almost makes you want to die. 

EDIT:

Found the below content here


  During the night, after Edward's emergency surgery was completed successfully, Alphonse discovered the true tragedy of his new body. Incapable of physical sensation and sleep, he began to feel detached from others and lamented the long solitude of restless night.


This clearly states his disability to sleep.