I'm pretty sure the trance state is probably due to either too much third eye awareness or too much energy up there. You can reach a trance state focusing on most any chakra, though I have to agree with you, the third eye one, is a bit too "spaced out" especially if your roots aren't in deep.
I think it basically means, your lining up with the energy of that chakra beyond what your body is normally used to. Focusing on "nothing at all" rather than "nothing in particular" definetly really increases the third eye trance state for me.
It definetly made me a bit too indifferent to much of my life happenings, having too much energy in the third eye, and almost being too "in the moment".
Third eye's great for showing you where to burn karma, which is probably why you have the irritability. POssibly too much karma burning at once. If you often feel heat in areas of your body, that's usually karmic blockages burning off. I reckon focus on balancing out the burning of past karma and the looking towards future growth, but both must be done in moderation.
I swear, yesterday was a too much future day for me, and today was too much past karma burning. Been pushing things a bit too much lately, and it can definetly make for much irritibality, as your body tries to hold on to all these truths you're instilling and untruths you're letting go of.
I've been reading the Dhammapada lately. I love how it helps me keep in mind to balance both the future and the past, but in a slow but steady sort of way. It's\\ always sort of a gentle loving forgiving and growing sort of energy I find I get by reading slowly and introspecting a little bit while reading. But all must be done in moderation... which Im still learning.