I've never heard of a term for what you're talking about but it sounds like someone with an incredibly high level of hypnotizability or ability to enter altered states of consciousness. If this state is entered by conscious choice, then it is almost more like a state of deep meditation-- which is also a dissociative state and/or altered state of consciousness.
If it is a chosen state, I would suggest that you do more research on meditation and states of deep relaxation/mindfulness rather than searching through the literature on psychological disorders. If it is a state that is entered without conscious choice then it is more like a catatonic state; catatonia can be due to a number of different psychological disorders including deep depression and/or a psychotic disorder.
You mentioned that your mother was neglectful- did you have other caretakers who were more attentive? Neglect is a very powerful form of abuse and can create symptoms similar to those created by extreme abuse in children. Your dissociation (especially given that it started at 9 months old) sounds like a trauma-reaction more than a conscious choice to enter a meditative state.
Now that you're taking better care of yourself as an adult and are entering this state less often, have you noticed any patterns as to when you go into it? My guess would be that it would be during times of stress. I would suggest that you work with a therapist to understand this a bit better- understand its relationship to your childhood/family, and also understand how to keep it from happening now.
I don't know of anyone who shares the same kinds of dissociative experiences as you are describing. This does not mean that no one else exists, just that I have not worked with anyone with this exact condition and so do not know a name for what you're describing.