Ready for sleep (5)
(Other definitions for tired that I've seen before include "In need of sleep" , "Physically or mental weary" , "Zonked" , "Physically or mentally weary" , "Whacked" .)
(Other definitions for in bed that I've seen before include "as 15 Down [GARDENERS] may be?" , "10 [AT REST] ," , "Lying, possibly" , "Not yet up" , "Retired?" .)