Ungrounded power meant that you may be an inexperienced meditator, you may be inexperienced when working with your personal energy, and sometimes what happens is a newbie will have a lot of energy flowing through them, emotional energy, spiritual energy, etc., and instead of having this energy ground into the Earth or project into the Universe, the person's body will kind of shut down, like a short circuit, and they'll fall asleep.
This is usually very harmless and is just your body's wisdom taking control. By practicing meditation and basic energy techniques you can avoid this.
As far as omens go, magic is a highly symbolic act and therefore i think all feelings, visions, and actions are little hints as to what is happening, the success of your working, etc. I think there is very little coincidence with spellwork.
I have had candles i was lighting for specific people that just did not light. I have worked a million candles, and when one doesn't work, it makes me take notice.
I almost burned my house down when making a mojo bag for someone wh was deeply troubled. I have made a million mojo bags and i have worked with open flames daily for over a decade. I have never even come close to burning my house down.
I have had a glass-encased candle explode while i was standing over it. These candles are made to be burnt unattended for days straight. I frequently have several going at once and have for years. They never explode.
These are three examples of "coincidents" that happen during spellwork. They were very very instructive as to the outcome and circumstances of each situation. I think falling asleep before your spell was cast may be another example. Maybe not. You would be the best judge of that.