The image of a domme is a common one, many men have that fantasy even if they are not submissive or BDSM orientated. Just look at how many times it appears in fiction - Catwoman, the Charlie's Angels film, The Avengers.... So seeing it is not so unusual in any of the forms described above. What happens to a sub is another matter entirely and yes that may shock...

Though the purpose of these documentaries is usually to shock, even if they often fail (at least to my mind... but I have always known that I am hard to shock with anything sexual ). The one I saw had some quite explicit scenes of sessions with Mistresses and subs and gave examples of some of the more unusual and controversial fetishes (a white man who wanted to be treated as a slave by a black woman and another who had a big Nazi fetish, for example). Though the closest they came to what I would consider a real BDSM relationship was a Mistress who brought her female slave in for a free session. That scene was very intense whereas some of the others came across as 'mere playacting'.

If you do a search online for 'Fetishes' and 'Channel 4' you may find it or at least a reference to it. I know Channel 4 have put a lot of stuff online as downloadable recently though this was many years ago so it may not be available.