Let's face it; sex can be messy. All kinds of awkward things can happen when you're getting hot and bothered. Farting and other bodily noises resulting from vigorous activity where air is being compressed in unusual ways can occur at the height of passion. Bad breath, excess sweating, stray bits of toilet paper, an errant hair, or leakage of bodily fluids can all can produce unexpected interruptions and embarrassment.
Sex can also create more concerning situations for one or both of you: a painful position, cramps, someone's hair being painfully pulled, or, the ultimate disaster, one of you being unable to perform in the expected and desired way.
No matter the level of awkwardness or disappointment, how both of you respond says a lot about your relationship, both present and in the future. For the lesser interruptions, the ability to laugh and say "excuse me" will allow both of you to acknowledge what just happened but then move back to the intimate moment at hand. For anything more serious, you will want to address the events in a safe and caring way, preferably at a time when both of you aren't so vulnerable