I don't think it's terribly common, but one symptom of MS is a tendency to exaggerated emotional response. For instance, extreme sadness provoked by something that only moderately sad (losing your keys, say), or unhinged laughter at something that's only moderately funny (Billy Crystal, say). There are different degrees to the phenomenon; at the extreme end is something called pseudobulbar effect, where the emotional response may bear no relationship to external events or the patient's real feelings.
Today, on my way back to work after visiting my podiatrist (I've got flat feet, probably secondary to MS, which has affected my balance), I was listening to Caetano Veloso on my iPod. On his album, A Foreign Sound, he covers a bunch of songs in English, including Dylan's "It's Alright Ma" and Nirvana's "Come As You Are." It's uneven, but has some gems.
Driving back to the office, "Something Good" came on. At the time, I recognized the song, but couldn't place it. (It's from The Sound of Music.) The lyrics are terribly sappy, of course. Without quoting them, the message is basically, "I was never a great guy, but at some point in my life, I must have done something good, because there's this other person who is fabulous and who loves me." I found myself crying at a stop light.
Later, I was perusing boingboing, which had a link to these hilarious fake romance novel covers. Sitting at my desk in my office, laughing so hard that stuff came out of my nose.
Is "Something Good" that good? Is "The Blind and Buttonless Horseman" that funny?