I've been meditating daily for at least 30 minutes
Not that time is the definitive factor, of the attainment of a state of insight, but that's really short for equanimity! Practice doesn't really start until your doing one hour sits.
I think I've reached equanimity, and potentially high equanimity.
Hey it took me ages to realise what i thought high equanimity was actually high equanimity, fortunately I had the help of two, highly accomplished Sayadaw's, who corrected me, and which I eventually came to realise as right.
It was like someone cleaned my head out, and my awareness felt limitless and I was extremely calm, though it was hard to concentrate on anything specific (like someone talking to me). This lasted for about 15 minutes before I came back to my usual self.
Definitely a Jhana like description, some people describe these kind of affects as soft jhana, as 15mins is bloody short. I would hit the space and calm, with no sense of body and sit in that for at least 45, but investigating that, I could pull out of it and return back in to it. Also you can hit equanimity as jhana, and that has a spacious quality that is still present with the body. A pliancy of body will occur, resulting in great easy after sitting for extended periods, i.e. 1 ½ hrs. While on my first three month retreat, I would often slip into these kind of jhanic states alternating between insight and concentration, its the natural result of high effort!
Also i should state, that this notion of jhana is a relative term which can be described as jhanic factors and samadhi rather than jhana. here are some links.
http://www.dharmaoverground.org/web/guest/discussion/-/message_boards/message/3626340
http://hkims.org/documents/bodhi-jhanas.pdf
Kamashila's MapThis exact same process occurred over and over again in the same sit - probably about 6-8 times. Effortlessly cycling through jhanas (as I think they were), reaching some climax point, then a jolt of energy that pulled me back to the beginning.
Don't get to caught up in phenomena, just practice. One significant point is that there is a real difference in retreat. I would hit states or point in short practices and could do that sometime consistently. But I found out that in retreat in deep practice there states had to be earned and ceased to become as available. This is because there is a centre of gravity and a peak, and in retreat you are pushing the centre of your gravity (which is usually dark night for me as it is hard to hold equanimity as the centre of your gravity) up to you peak. Its easier to jump around between different insight stages out of consistent & intensive practice.
From my description, does it seem like I was passing through the jhanas?
Some of that cycling stuff you where noticing sounds like moving around through the effects of different soft jhanic states, I prefer to call them factors though. Soft jhana or jhanic factors can be influences just as one can generate metta joy or loving kindness peace calm or equanimity. In the early stages of my practice there was not as clear a distinction between calm and equanimity!
You have some really good grounding in your practice to develop better samadhi and also insight, please look at some of those link above to better understand jhana and some of the different view around it.
Kind Regards neem