I'm sorry about your friend Hetty, that's terrible. I don't know anyone who has died from it but most of the long term residents here have had it at least once. This is my first (and hopefully last) experience with it.
The fatal type of dengue is when it goes into the hemorraghic type. I don't think they know for sure why that sometimes happens. I've heard it can be due to repeated exposures to the regular fever, to exposure to more than one sub type... I don't know. It's always more dangerous for the very young and the old, unfortunately I'm now moving into that second category. If you just get the fever without the bleeding, it is rarely fatal. It's just that there is always a risk it will go the other way. I'm pretty much back to normal now but it took me about 6 weeks to get my usual energy and get up and go to return.
