- chemical (diet)
- electrical (nervous system)
- mechanical (musculo-skeletal)
Nervous system is more than brain and mind; it involves growth of sensory awareness and control of movement; growth of feeling awareness, the ability to make subtler and subtler distinctions, and sense of control of action/behavior, of navigable memory, of flights of imagination — and to leave off all of these.
The "loss" of the physical body in sleep is FORGETTING the constraints of the waking state through a psycho-physical inhibition process electro-chemically generated in the physical body. It's a suspension of attentional-intentional memories associated with the waking state, revealing the "subtle" body. That inhibition continues into the dream state.
When the memories of eros and agape (imagination and memory) are inhibited, the rest/equilibrium state perceived is called the causal body.
Thus, the four basic somatic functions, attention, intention, imagination and memory, when inhibited, lead from the waking state through dream and deep sleep.
The matrix of the three states may be somatic — or soma may be the "outer picturing" of the harmonic content of the three states. "If you want to know the past of the mind, look at the body; if you want to know the future of the body, look at the mind."
Soma isn't just flesh; to think so forgets that all matter is embedded in fields. Soma consists of both matter and field. It is very tempting to leap to, "physiology is the matter" and "sentience is the field". But I won't say that.