You have to acknowledge that as appropriate as tears may be for loss, so too is laughter. Maybe not the actual act of a person dying -- if you find yourself chuckling over car wrecks and leprosy, you may want to seek professional help, because you're a bit of a creepy ghoulie, aren't you? However, it's worth noting that you don't need to deal with death by becoming an emotional wreck.
In times of stress, I become almost unbearably goofy. I enrage others in tense situations due to my tenuous grasp on seriousness that becomes more and more ephemeral the angrier people get with me until the point where I either get hit or have to hit someone else. I'm not proud of it, but it happens. I will smile like a drunken Cheshire Cat making it rain at a strip club when the s**t hits the fan and have little to no ability to somber up for the sake of maintaining decorum. It's not necessarily that I think it's funny if someone died, or you lost your job, or the city is being locked down due to the presence of mutant isopods -- it's just my natural reaction. I suppose on some level even my writing is an outlet for that, for my desire to make people laugh. I enjoy it, I want to be entertaining on a basic level, and, even when wholly inappropriate, I still try to do it.
Now the problem here is that I am acknowledging it as wholly inappropriate when I don't even feel it's inappropriate. I feel that others feel it's inappropriate. But there's plenty of evidence to indicate that not everyone thinks you need to wear black and mope around in the face of death. A mourning period, a time of sadness to reflect on pain and loss, is normal, but at a funeral, for instance, you don't need to all be weeping to "Amazing Grace" and wishing Grandpa Cankle godspeed. If he was a happy man in life, celebrate his death. Tell funny stories. Put on his favorite obscene puppet show. Show that super-8 film of him and three hookers in Saigon. Whatever he would have liked.
Our sadness comes from a sense of loss, but there's just as much precedent to experience joy when you reflect on what you had and what made that person so important to you in the first place, and in the end, you're likely to feel better making death a final celebration of all the experiences you did have, rather than a lament of all the ones you won't.