Meditation - Visualisations and Reality

Here's a brief synopsis around types of meditation, although the author is biased as the article promotes the heart meditation over the other types... Types of Meditation.
Within Druidry the usual type of meditation is a form of Guided Visualisation with a western mystical focus, typically a type of Kundalini meditation on the light body or internal cauldrons, see Erynn's excellent text on the Cauldrons of Poesy, which precedes the Guided Visualisation and enables the practitioner to settle into their meditatory context before the Visualisation.
During a self-guided visualisation meditation the question arises around one's experiences within the visualisation - do they come via a connection to some 'Otherworld' or are they just made up imaginings from the brain? Usually there is a tone of the sarcastic modern atheistic sub-text or rationale that it's all just from a fevered imagination and thus without relevance or importance to the person or the 'real world'. Given that our experiences within the Guided Visualisation may well include advice and guidance for the 'real world' from beings met within the 'otherworld' the question of it's importance and reality do need to be addressed.

This understanding of the inner meditatory world fits into the grey area, I believe, of the transrational. One of the things that I like about Druidry is the lack of a defined position on this. Each Druid has to reconcile their Druidic transrational experiences for their self which leads to the 'herding cats' approach to Druidic dogma, no two Druids will agree as each Druid has reconciled and understood their inner world themself without the intervention of some priest to tell them what to think.
So does my brain just put an imagined experience into the meditation? Are the spirits real and is the otherworld really there? Does it matter?
These are big questions and maybe breaking them down into bits will help:

1. What do we mean by 'brain'? Brain could mean the conscious, subconscious or the physical grey stuff. I think it means our whole being, our physical and non-physical self, in this context
2. Then there's 'put' - even if we take the atheistic worldview you could view it as 'access' rather than 'put'. 'Put' implies a conscious act of creating something without a basis in the real world, however, I think that 'access' is closer and suggests that it's from the subconscious which has a basis in a real world that our conscious can't get to
3. And also 'spirit' - which is a definition that can be argued about incessantly. For me I think that spirits are energies or patterns that bubble up from within our subconscious. I do not know how they get into the subsconscious
4. Finally 'does it matter' - I think it's part of the Druidic experience to come across these transrational questions and to try and find a reconciliation that satisfies you. Personally I think it is important and that yes it does matter. It is how we access a deep and ancient wisdom via a subconscious mechanism. How that subconscious mechanism works I do not know - it could be linking deeply held genetic patterns or some Akashic record or there really could be an otherworld or higher plane that is accessed

For me these 4 questions are the big areas of Druidic / spiritual work. I wrestled with them through the whole Bardic work and they form (for me) the part of 'working it out for yourself' that is important to the Western Mystery Tradition as opposed to the revealed dogma, interpreted by priests, of the big 3 religions.