What is the ruling on the emission of prostatic fluid (madhy) when feeling a sense of humility and awe (khushu') in prayer, or any other act of worship?

There is no necessary connection between feeling devout humility (khushu') and the emission of prostatic fluid (madhi). What you are feeling may be a delusion from Satan. Do not conclude that madhi or anything else has exited unless you have absolute certainty. Rather, assume the default, which is that nothing has exited. This is supported by the hadith: "He should not leave (his prayer) until he hears a sound or perceives a smell."