For the final scene [of Castrovalva], the script called for Adric to look “pallid” as he was still recovering from the effects of imprisonment by The Master. According to the commentary on the DVD, this was accidentally achieved by Matthew Waterhouse, who had a hangover from the night before from drinking too much Campari. Whilst the cameras were filming The Doctor and Tegan in conversation about who landed the TARDIS, Waterhouse was vomiting behind a tree. The other actors, to their credit, continued acting despite it so the take could be used.
Look what I just saw on Facebook!!
■ A Walk Down Memory Lane with Peter, Sarah, Janet, and Mark ft. Matthew
He’s even wearing a hat I’m gonna sob.
*inappropriately loud laughter*
From The Doctors Revisited: The Fifth Doctor
why am I only just learning that they got Matthew to come back for this
Matthew Waterhouse, Four to Doomsday commentary
(There’s context to this quote but you know what, I’m just gonna leave it here as is.)