I'm going to pick on this definition, because it is not possibly true since I am the one writing this.The definition I am using comes from http://www.thefreedictionary.com/persistent+vegetative+state. There are many others, but this uses the word, "irreversible."
persistent vegetative state
(Medicine) Med an irreversible condition, resulting from brain damage, characterized by lack of consciousness, thought, and feeling, although reflex activities (such as breathing) continue Abbreviation PVS
If this was "irreversible", then I wouldn't be writing this. I was thinking the definition of MCS, minimally conscious state could just be tweaked, but you will see this, too, will need major revision.
|Minimally conscious state|
|Classification and external resources|
Auditory processing can differ between MCS and PVS. fMRI response to the patient's own name has been suggested as a technique to distinguish between MCS and PVS.
PrognosisPatients with severe brain damage may progress through stages of unconsciousness with eyes closed (coma), to unconsciousness with eyes open (vegetative state), to a stage of "inconsistent, erratic responsiveness" (minimally conscious state). 
It is not known whether patients in MCS can process emotion. MCS is thought to have a more favorable outcome than persistent vegetative state.
Doctors in the USA recently succeeded in bringing a man who had been under MCS for six years back to consciousness by planting electrodes deep inside his brain. 
I see PVS as occurring on a linear progression of consciousness. It occurred in me prior to MCS.
_____________________________________________________________________>>> COMA PVS MCS EMERGING CONSCIOUSNESS
What I experienced was closer to the diagram in http://www.coma.ulg.ac.be/inform.html. This lists Locked-In Syndrome (LIS) as a separate state. LIS can be separate, but in my case it wasn't. It was intertwined with the PVS and MCS states.