Hi jcb123,
I experience the exact sensations you describe and have been able to do so voluntarily since I was about 14. I'm 29 now and just this evening thought why not have a look to see if anyone else can do it. Obviously quite a lot of people can.
From what I can gather (I've only just started looking into it) the feeling is caused by stimulation of the pineal gland which is located right in the middle of the brain as it releases melatonin.
There's an enormous amount of information available on the internet about this from all sorts of angles. Loads of spiritual and metaphysical beliefs in various cultures for hundreds of years seem to grant the pineal gland a unique significance in that it acts as 'the third eye' and allows us to 'see' far more than it's generally accepted we can.
Most of the information I've found relates to meditation and reaching higher spiritual planes or gaining awareness of other dimensions.
I'd rather not dwell on that to be honest because I find it rather difficult to take seriously. I'm more interested what the effects of pineal gland activation have on the body and on itself over time if it's practised a lot. I gather that it is a gland which calcifies (don't know if that's good or bad), has links with sleep patterns and affects skin condition.
Fascinating though it is to read into the fantastical and exciting promises of interdimensional mind travel I'd really like to try and understand what the scientific implications of being able 'to open the tap', as I think of it, really are.
Basically is it good or bad for us? Does opening the tap preventing it calcifying or cause it to do so, make us sleep better or worse or make our skin age faster or slower? Why can we do it?
I can't seem to find any solid acknowledgement from the scientific community that people can do this and I suppose that's why most of the 'information' I've found relates to more alternative takes on it's implications.
Here are a couple of links to pages which have 'information' on the subject:
https://en.wikipedia.org/wiki/Pineal_gland
https://www.crystalinks.com/thirdeyepineal.html
Ed, London