[Black Sheep]

I'm not sure if you mean waking consciousness as in visibly awake or just mentally awake as your body shuts down.

It certainly helps, and can lead to wonderful experiences, akin to travelling to a destination and waking up there or alternately watching all the sites and sounds as one travels.

Let's say that how one dies(or reacts to the transition) is akin to an accumulation of who one is or has become in that lifetime, just as in each moment in the now. Speaking from my own experiences, and beliefs thus formed....I'm one of those persons that believes state of mind has importance during the dying process, many things happen, and may pop up. It helps to be familiar with them, as to not react in fear. If a person dies in an angry state of mind, it can lead to similar feedback, so rather than dieing peacefully, frightful scenes appear. Saying a mantra, or focusing on one's favorite deity as TheTruth said can help in the process.

In regards to brainwaves, each person cycles through each of the brainwaves, just as in sleep. In coma, I imagine they have a head-start on the process, but do so just as all others may as well.

In regards to altered, I guess that depends on what you mean by altered, altered from standard beta mode? One can function fully conscious from alpha, theta and delta, and there are many adepts who do so.