The fourth dimension is probably TIME. As for the afterlife..... To make sense of it, you must realize that you and every other human being is an animal. And, all animals, all living beings, dream, astral project, and have an afterlife experience that varies in complexity but is essentially the same for all. Human beings are very complex long lived beings and so their afterlives are long and complex. The end result is the same for most, which is reincarnation. Some, however, are advanced enough to avoid reincarnation and to have other choices. This happens by avoiding what are commonly called The Bardo Realms. Realms of Illusion. Sounds mysterious, but its simple. When you are alive, at the end of each day you get tired, fall asleep, and start dreaming. When you are at the end of your life, you die, and after a short time you start dreaming. Once you start dreaming after you die, there is no way back until reincarnation occurs. So, the only way to avoid that and to have more choices is to stay conscious. Having some astral projection and lucid dream experience helps enormously here. Most people, when they die, are stuck in Real Time Zone for a few weeks. During this time they can visit family and say goodbye. This is when most spirit phenomena associated with recently deceased spirits occurs....the first few weeks after death. To have more choices, I expect the way ahead is to try to remain in the real time zone, and to remain conscious and in control. From here, you'll need to trust your intuition, and your higher self (aka God) for guidance. I recommend you meditate on how you are an animal and what this means. It helps to provide realistic perspective.
-Robert Bruce