If a spouse our lady friend were to walk in unannounced there would definitely be a startled something with a rise in blood pressure and adrenalin to boot. All in good fun brakel2, you know us naughty boys can't resist this kind of question.
This is however, providing one has a healthy, trusting, loving marriage. My blushing bride was having an affair and I noticed that she suddenly covered herself, when she didn't before; made sure her nightrobe was fastened before walking about, when she never did this before; locked the bathroom door while taking a shower, when she had never done this before, ect.
In my mind, if a spouse acts this way within a mature marriage it may be an indication that they have something to hide. Guilty consciences have a tendency to think that others see in them what they know about themselves.