headaches... energy flow or blocks?

It's certainly possible. Especially if you're not prone to getting headaches normally.

You might try going to an acupuncturist for a treatment. Just tell them you've been getting headaches when you meditate or something like that. After your treatment go try another session with your aneros. If it is an energy blockage and the acupuncturist was any good at all, chances are you won't get a headache.

You might also want to pick up a copy of Acupressure's Potent Points by Michael Reed Gach. It's a great way to learn how to treat these things yourself and it's easy to do. I've been using the techniques in that book since I was teenager. It's amazing how many times I've helped myself or someone else feel better in less than 5 minutes.

OK, I noticed I get a headache when all I do is use the bowel rinsing syringe. I thought it was maybe some impurity in the tap water so I tried distilled and still got the headache, so... that's more than I knew before. I still have to try the acupuncture/pressure points deal. Thanks, Pan!