You are fairly new, so I do hope you have been "lurking" and very well reading on Astral Projection and noting any potent and important methods of induction.
Yes, that is how astral projection is achieved. Some may naturally be more connected to their spiritual body or have issues staying stable and properly concluded to their physical body, only an issue of weakness in the silver cord, or astral cord as some refer to it as, and can not help but drift in to the astral plane without intention. Otherwise, consciousness is vital in astral projecting at will.
Methods of induction will differ, but many do use mediation as a light gateway to induction. So, you will want to be well aware of what meditation is, how it is done, and how you, most importantly, attempt and achieve it. Chakras may help, so unblocking these will do well, you can find many articles around the internet of it. Let energy flow properly through your body, and you should be spiritually and physically fit to astral project and expect encouraging results.
I have only astral projected once, but mine was involuntarily. Your point about the silver cord, it sounds like the white tunnel like arm coming from the center of my chest and I kinda just step out of myself.
I have not much of an understanding about AP but would love to hear more about this silver cord thing, or whether what I stepped through was the 'silver cord'?
Or whether what I experienced was an astral projection at all, but I do recall looking back at my body which is what gave the impression that had happened. Are there any factors involved too that cause an involuntary AP, because on this occasion it happened whilst I was drunk.
The silver cord is what connects your spiritual body to your physical body. It can never be broken, but can become weak. It usually becomes week when the chakras are disturbed, when your energy does not properly flow through you, or just because it is your first time astral projecting, and it needs to build strength.
You were drunk, and alcohol simulates the nerves excessively, and can cause hormone imbalance. Hallucinations are common when the nerves are stimulated greatly. And the fact that alcohol does stimulate nerves, means you are most likely the opposite if calm. Astral projection requires calmness because it does revolve around changing your consciousness to a higher and more functional level. Alcohol only lowers your consciousness to lesser levels.