The annihilation of the ego the merging with the one mind the connection to the all and to nothing. Or is it dropping your consciousness into your heart. Connect to the calm still point in your high heart.
This is what is called the zero point viewing the heart as a torus. Physically speaking it is pump of a iron rich blood bringing oxygen to every cell in your body. It is a bloody dynamo!
Maya the illusion that you are your mind your body you emotions. These evidence is all ego based and you are so much more than that. Otherwise things like reiki distant and remote viewing would not be things that could be done. Since they can happen our consciousness is not local or it can bilocate.
Getting back to Samadhi the adherents of the buddha say it is attained through deep meditation practice of many years. so through breathe work walking meditation or holding your hand in a mudra and stilling your mind until the state is achieved the loss of self. The connection to it all. the calm center of your heart. Serenity bliss all of this can be the reward.
Then there are the entheogens, the plant medicine and LSD. I have experienced ego death through the ingestion of LSD which was terrifying when I first experienced it but the feelings and visions I attained after that stage was indeed sublime.
In the end you can achieve the state in many ways for sometimes far to short. The trick is to be like the buddha and be in that state all the time. In the end remember that your soul is so much more than your mind your body or your emotions