Okay, this is a very complex matter and ties back into archaic mystery traditions that are very poorly understood these days. The very short form is that it's a bad idea to do this unless you have some very specific reasons for doing so -- and no, being nervous about death isn't one of them.
Under normal circumstances, when you die, you go through the normal after-death process and then reincarnate. This is appropriate and healthy, and keeps you from getting stuck in a personality rut; when you're ready to make the transition to not dying, that happens, and you stop incarnating into a physical body in a natural manner. Until you've reached that point, you're not prepared to function in a nonphysical body for more than brief periods, and you can mess yourself over good and proper by trying it.
A very long time ago, in the days of the long barrows, people from certain lineages used to voluntarily be buried alive in order to pass into nonphysical incarnation for a certain period, and serve as spiritual guardians of a place or a community. That was a duty and a sacred burden. Later on, with the rise of a warrior aristocracy and the replacement of the long barrows with round barrows, the same methods were hijacked by kings and nobles, and used in an attempt to cheat death. The results were not good. Over time, people stopped putting up with that -- the spread of cremation and the abandonment of mound burial are markers of this process -- and the techniques survived in a hole-and-corner fashion in the practices of vampirism. The people who entered into the earth in the long barrows were sustained by their own spiritual power; the kings and lords who were buried in round barrows (and, ahem, pyramids) were sustained by sacrificial offerings; those who practiced vampirism didn't receive offerings, so they had to steal life force from victims, usually killing them in the process.
So my advice is to focus on your own spiritual development and enter into the Unseen when you've matured enough to do it properly. The alternatives usually end in a real mess.
Re: Generating a Spiritual Body
Under normal circumstances, when you die, you go through the normal after-death process and then reincarnate. This is appropriate and healthy, and keeps you from getting stuck in a personality rut; when you're ready to make the transition to not dying, that happens, and you stop incarnating into a physical body in a natural manner. Until you've reached that point, you're not prepared to function in a nonphysical body for more than brief periods, and you can mess yourself over good and proper by trying it.
A very long time ago, in the days of the long barrows, people from certain lineages used to voluntarily be buried alive in order to pass into nonphysical incarnation for a certain period, and serve as spiritual guardians of a place or a community. That was a duty and a sacred burden. Later on, with the rise of a warrior aristocracy and the replacement of the long barrows with round barrows, the same methods were hijacked by kings and nobles, and used in an attempt to cheat death. The results were not good. Over time, people stopped putting up with that -- the spread of cremation and the abandonment of mound burial are markers of this process -- and the techniques survived in a hole-and-corner fashion in the practices of vampirism. The people who entered into the earth in the long barrows were sustained by their own spiritual power; the kings and lords who were buried in round barrows (and, ahem, pyramids) were sustained by sacrificial offerings; those who practiced vampirism didn't receive offerings, so they had to steal life force from victims, usually killing them in the process.
So my advice is to focus on your own spiritual development and enter into the Unseen when you've matured enough to do it properly. The alternatives usually end in a real mess.