I'm rereading parts of Huston Smith's
Forgotten Truth, an exposition of the shared worldview of the traditional religions. One thing I notice is that he places the demonic realm also in the sphere that transcends and includes the ordinary world - basically demons are of the same category as angels. Fr Seraphim Rose in
The Soul After Death also referred to the demons usually as "the powers of the air", and portrayed them as superior to us humans in our earthly lives. Likewise Ryuho Okawa places hell in the 4th dimension (compared to the third dimension of the mortal world). In his book
The Challenge of the Mind he strongly warns against opening the mind to the spirit world without first repenting our wrong thoughts of the day and as far back as we reasonably can remember. Otherwise our mind will be in tune with "stray spirits" (their name for demons) rather than High Spirits (angels, saints etc).
If you are a materialist, none of this matters. In a manner of speaking you are lucky then, for the damage you can do to yourself is also limited. But today there is a wave of spirituality, in which people reject outright materialism but also organized religion, and seek personal spiritual experiences. Unfortunately newbies on this path may be unaware that some things are higher than us but not better than us - quite the opposite.
In psychological terms - which the religious person will see as the shadow play on the cave wall cast by a higher reality - you venture into your subconscious through such practices as meditation. Your subconscious is probably not a nice place. This depends on your life up to now, and your upbringing, but there is also a common human element. It is certain that you have a shadow. This is the human condition. And depending on your mental disposition, venturing alone and weaponless into the subconscious is a dangerous undertaking.
I am a big fan of trust in God, but although God is spirit, not every spirit is God. There won't be just flowers and kittens if you embark on a spiritual path, at least if you go beyond the slightly stoned feeling of just letting go of your everyday thoughts. And sometimes that is enough. When I was young, I eagerly proselytized for meditation, but most of those friends who tried did not enjoy it. In fact, found it creepy. I realize now why. And I no longer recommend meditation without some framework of theory and preferably a community.
As you travel past this intermediate realm, however, goodness predominates, closer toward the Source, the Ground of Being, or just plain God. But will you find your way there? The only reliable way I know of is being pure at heart. But that has proved surprisingly difficult, even with a good upbringing.