All I can find on this image is that is made by a Visual Novel graphics artist called "Makita Maki".He seems to have a lot of original drawings unrelated to any VN,anime,manga,etc...so this one could be one of those original drawings.
I think they refer to their composure or mental state.When overwhelmed with pleasure they often say it to point out that any more pleasure will drive them insane or..."break" their mind.I could be wrong though but that's what I picked up from what I saw so far.