Abstract: A support unit for a modular head support assembly having a right support post and a left support post, said support unit comprising: a support body; a right attachment element and a left attachment element configured for articulation with said right support post and said left support post, respectively, said right attachment element and said left attachment element being disposed at opposite sides of the support body; and an adjustment mechanism configured for selectively adjusting the position of the right attachment element and the left attachment element with respect to each other, at least from an extended position towards a retracted position.