Are all of the people around you wearing black dresses or black clothes? Are they all there to remember you? Perhaps you are worried about your own health or well being if you are dreaming that the world is attending your funeral. This is a possibility too. Hopefully you will not come down with anything serious. A dream like this is often just a reflection of an uneasy attitude. Try to relax a little more often and things should be just fine for you in the future.
If you have a dream in which you are the only person that is wearing a black dress, this might mean that you are feeling some sort of connection with death. At some point everyone in life questions their relationship to death and what it means for them to die or for anyone that matter. At some point people have to come to an opinion of what it means to be dead and the answer is going to be different for everyone that encounters this line of thought. Perhaps this is what you are thinking about. Then it is no wonder that these are your thoughts. Maybe you are just at the point in life in which it is time for you too to question your relationship to death.
To dream that you are wearing a black dress also shows that you are mourning someone. Has someone close to you died recently? This is the most common reason that you would be thinking about death or wearing a black dress in your dreams. You think that it is time for you to mourn the passing of one of your loved ones. It is even possible that it was not recently that a person died. If you go around and go over the death of someone close to you in your mind enough times then you will eventually start to think about what a good person they were and then these thoughts will immediately translate into thoughts of missing them and then these thoughts too will translate into thoughts of mourning.
When you think about the presence that someone important to you had in your life and the difference that they made for you it is hard not to consider how sad their death was. Even if their death was relatively peaceful and they lived a long fulfilling and happy life, it is still appropriate to mourn for them because you went on living after they had died. As corny as it is to think about though, you have to remember that you act as a bit of them when you are in the world today. Whatever they passed on through you, memories or whatever, that is all a part of you now and you need to remember that if you want them to truly live on through you after they are dead. This would be the greatest service to your loved one.