I feel like I'm bleeding into someone else, like colors running in the rain. And it's completely involuntary, which is why I have to make a concerted effort to avoid toxic people, no matter how attracted/drawn to them I am because I can get enmeshed so deeply with them down to a cellular level. It's like being under a spell. I've depended on my friends and my sister to jerk me away from the fire when I get entranced. I really do need their help. The complusion to "merge" is too strong for me to overcome sometimes. As I've gotten older, I can brace myself and hold onto something and escape the black hole, but it comes at a big price. Avoidance of (or never knowing) these sorts of people is key. If I can't, I have to dig deep and say NO NO NO in my mind until I can step away because the compulsion to merge is that strong - like getting into their brain and their soul and reading their inner mail.
If it's a good person, then it's a mind-meld. As someone else said, I want to crawl inside their skin. I can tell when I'm responding to another sx - the vibe is specific, like two bodysnatchers. And it can have zero to do with sex, as such. It can be a soul connection, a powerful merging of spirits and minds. I have many of those. The physical only enters in when there's a mutual chemical/bodily attraction. When that happens, it's like being knocked right off your feet.