Question: Sometimes when I'm focussing here (between the eyebrows), there is this feeling of expansion. Is that just an illusion and you ignore it?
If it is totally peaceful and quiet, then that is good. That is how the consciousness expands and realises one day that it is all pervading, not simply hidden into one single body. That is how the expansion happens. If you are feeling peaceful and as quiet as possible, then continue with it.
Question: Sometimes I start thinking, what is this? Or what is happening?
No need to worry, because if you try to think, then mind will get into imagination and that comes back again. Just watch it, peacefully.