Yes you can learn to do it again. I have astral projected a large number of times and I was always able to get back to my body. Supposedly, there is an etheric cord that connects your soul to your body and so you are never fully separated from it. Here is some information on it:
As far as dangers…I have only had problems with negativity during sleep paralysis. When I have projected though, sometimes I might feel really tired or heavy but there is nothing dangerous around me. Sometimes I feel really light and free. Both these examples I think are within the physical realm. I think the physical realm has different levels, maybe the ones closest to the physical ground are heaviest. I don’t think negative entities are there because it’s not the realm that they exist in. I am not sure on that though.
But to insure that you have no problems, just make sure your room is clean and your bedding is clean. Make sure that there isn’t anything under the bed and if you store stuff there, make sure that it is organized and not just cluttered. Keeping an amethyst by your bed (or wearing one) will also provide you with gentle spiritual protection and also help you to project.
Here is an article on the dangers of astral projection:
Use your own discretion on the information I gave you. Not everyone’s experiences are the same and some people have more built in protection than others do…sometimes because of past life experience and maybe sometimes because of how spiritual they are in this lifetime.