Subspace is obvious different things to different people. For me it is like that moment when I organism and all the pleasure of the ejaculation comes rushing down on me and I get flushed and just a bit shamed, especially when masturbating, because it's a "no no." However, it is also the same feeling when I am just humiliated or embarrassed: warm flushed face, racing heart beat, just want to escape into the rabbit hole and disappear.
That is the basis of my subspace. I can put myself there and do put myself there a lot without anyone knowing I'm there. However in BDSM situation or even other sexual encounters, that helps me go deeper and deeper in to the subspace trance.
When I masturbate, the most sex I ever had and in the old days five times a day was not uncommon (after heart surgery I've finally working my way up to three times a day!), my fantasies in my mind take me to places where I remember past true experiences yet new inventions based on real events or stories I've read like on here.
I might imagine I am the victim of a crime I heard of where I don't condone what happened to that person but secretly wish I were them. For instance, at a hotel one day I overhead a security detail talking about an incident where a husband got mad at his wife and pulled out his dick and pissed all over her.
I couldn't get the image out of my head. I felt bad for her and felt the guy should be punished because she didn't agree to the abuse that was criminal. I though secretly wished it had been me forced to endure that treatment, although I would never really want it to be that way.
I have been peed on and drank piss from the tap many times since. Every time I do my mind goes into subspace because I feel that I am being forced to do such as nasty thing. I have no control over it, even though I do.
So subspace for me has a component of giving up my body to the sex act, doing things I wouldn't give myself permission to do. Sort of an out of body experience. I stand over myself watching myself doing "bad" things, even things I like.
Even when I wear panties under my clothes or even better a diaper, I have that same humiliation and feeling of being forced to do it. When I pee my diaper in public, even though voluntary, my mind takes me to a subspace where I am being forced to do it by some unseen force.
The ultimate highs in subspace I ever achieved was when I was with a BDSM couple and was active in a local BDSM group. Although we had safe words (which I rarely used! What's the fun in that?), I still would put my mind in subspace that I was forced to be there and couldn't escape.
True bondage reinforced that although again, it wasn't really real, I could halt on a single word.
I really don't like spankings, but when I was spanked my subspace would kick in high gear and the out of body experience took over.
I do like sucking dick, but anytime I suck a dick I mentally go into subspace like I'm being forced to do it even though I'm not.
The pros are that I have had some fantastic natural highs. The cons were, especially when I was in the scene, I could have some serious downfalls from that space, leaving me depressed and sullen because I knew I really could never have want it seems I wanted: true sex slave status. (All sounds good in fantasy but would never be truly possible!)