I will first encourage you to not be alarmed or afraid. And perhaps you are not. I have had 3 dreams in which I died but there was never a feeling of panic or fear. The feeling is the essence of dreams. There are times when upon waking you will talk yourself into a fearful state but try to stick with the dream feeling. There are many reasons you could have this dream, only YOU will know for sure.
Dying is a metaphor for rebirth. Having a complete change in your life and being successful with the change can bring about this kind of dream. A clear message to yourself that it’s over and done, time for rebirth and starting anew.
The scene is important as well. There is a chance that as you travel out with your subtle body into the astral plane that you joined with a memory of another lifetime or parallel reality in which you actually had experienced something like that. Perhaps you were in a foreign country with no one familiar, wearing clothes you don’t normally wear. In this case you would have to ask yourself, “Why have I revisited this memory?” , “What can I learn NOW from that experience?”.
Another way to look at it is with the symbology itself. As in a play on words. Shot in the back is like a stab in the back. Is someone in your life doing that to you metaphorically? Do you have a co-worker, friend, or partner who is shooting you in the back?
The dream indicates a strong message to yourself. Whatever the message is, it is a last ditch effort, if you will, to make the idea known to you from your higher self. If you are strongly connected to your dreamtime there is a good chance that the previous dreams and future dreams will elaborate on the concept. Ask before you go to bed for more clarity on the dream.
Look at the feeling, the sequence of events, people involved and search your inner being for the message.