The reiki healing session sounds like a mind altering experience which is now becoming stressful for you. Personally, I don't know too much about reiki but I am what you'd call a spiritual kinda gal.
It may pay to do a follow up, just for advice. Whether you contact that practitioner or a reiki master who has greater knowledge, I'd imagine they'd be able to tell you what's going on. Definitely keep looking for answers and support. I say this from personal experience. In a nutshell:
About 15 years ago, I was in depression group therapy when suddenly I found myself coming out of a decade and a half of depression. Whatever the exact trigger, it was like a switch just flicked in a split second. In this moment, my mindset suddenly began to change (in a positive way). Then the changes started becoming pretty intense to the point where I phoned the therapist who was facilitating the sessions, as I didn't know what was happening to me. She was of no help at all. I wish I'd kept looking for guidance, as the weeks that followed became seriously mind altering. By the way, all settled down after a number of weeks. When you don't know what's happening to you, things can get scary. Guidance is so incredibly important.
When an energetic shift happens it can become mind altering, kinda shifting your 'reality'. The question becomes 'What is my mind doing?' Some might suggest it's opening. You're becoming more open minded. What you want to do with an open mind is entirely up to you. Strongest advice - Be careful what you let in to an open mind. An open mind may dictate 'It doesn't matter about gender when it comes to the kind of energy you want to explore and experience with another person. Don't let the concept of gender limit you'. Some people insist on putting a label on this way of thinking and label it 'bi-sexuality'. Consider the energy (you're attracted to) instead of focusing on the label that society defines it through. Everyone has a different energy about them.
May sound a little strange but I can't help but wonder whether you're attracted to masculine energy, not men. Would you say you're attracted to wanting to be more direct, assertive and action orientated and you feel more drawn to this nature? They say every person requires a balance between the masculine and feminine, the Yin and Yang. Exploring and finding the perfect balance within yourself may lead you back to your love of women. This could be a 'recalibration' period you're experiencing.