I've heard some scary stories about potential bad outcomes from meditation. These outcomes seem to mostly be from people practicing insight meditation for very long periods of time, though.

So I figured, hey, a few minutes here and there of loving-kindness meditation should be totally fine and not scary, right? I've never heard of anything weird or out-of-model happening to your brain from just sitting down for less than an hour to think about how much you love people.

Wrong!

I had a strange and slightly frightening (though overall positive!) experience on just my third time doing loving-kindness meditation. On the prior two occasions I'd done it for less than ten minutes at a time. This time, I decided to hold out and do it for longer -- at least half an hour, or up to an hour, the full duration of the Quaker Meeting for Worship session I was in.

(I usually do something very different in my head during Meeting for Worship, which isn't meditation at all. I'll probably write more about this later.)

In the first few minutes, I had similar experiences to what I'd felt before. I focused hard on the sensation of compassion and empathy, which was difficult, but felt good.

Then I started having more success. The feelings of love and compassion grew stronger as I found better mental focuses. I was focusing on some memories of my infant son laughing, smiling, and playing with me and my spouse.

After a while, the feelings dimmed. It seemed like I had "used up" the power in some of these memories, so that they didn't trigger the same effect in me.

But I kept going, and the feelings started intensifying once more. It felt better and better. I started thinking about feelings of love and compassion towards other people in my life, even people who had annoyed me before, and I started to feel transcendently, uncontrollably happy. It was great. But then it kept going. Suddenly the feelings kept on getting more and more powerful without my having to do anything. It felt like there was a balloon of happiness inside me, swelling and getting larger and larger.

This was the point at which I got scared.

I felt like something strange was about to happen, something I couldn't understand or control, and I was absolutely not okay with that. I did not want to find out what would happen if the balloon popped.
 

So I opened my eyes and did what I used to do when I had panic disorder: I tried to ground myself. My breathing was fast, and I slowed it down. I looked around at the other people in the Meetinghouse who were still sitting calmly. I reminded myself that there was a world around me and I was going to be back in it.
 

The balloon subsided.

I was able to bring myself back to a normal-ish state, but I felt physically shaky for the rest of the day. It felt very strange talking to other people, yet also easier and more fluid than normal. I started saying "I love you" to my son much more often than I did before.

For the rest of that week, just by concentrating briefly, I could bring back some of the physical sensations I'd felt during the intense meditation session -- a warm glow in my chest, flowing outward to the rest of my body -- and re-ignite some of the feelings of love I'd felt.

The most intense effects died down after a week or so, but I think I've retained some of them even now. This was about six months ago.
 

I researched and asked friends who do meditation about what, exactly, was happening to me. It sounds to me like I came very close to the "Arising & Passing Away" described in Mastering the Core Teachings of the Buddha. I was very worried for a little while that I would experience the depressive and unpleasant side effects described in that chapter, but I never did; this, plus a few differing details, makes me think that my grounding technique averted my actually experiencing an A&P event.

Some of what I experienced sounds similar to "jhanas". It would be odd for me to have attained a jhana after so little practice, but I suppose it's not out of the question.

I do wonder if I had any predisposing factors that would have made this more likely. I have sometimes wondered if I have bipolar II disorder (I've experienced what I'd call depressive and hypomanic episodes, lasting a month or more), which could be a factor. I've also spent lots of time in Meeting for Worship throughout my life, which isn't meditation, but might cause some other changes to one's brain. Lastly, my son was only four months old when this happened; it's possible the intensity of hormonal changes and feelings that come with being a new parent made this more likely.
 

I'm overall happy that this happened, and I've continued to occasionally practice loving-kindness meditation since, but I'm also very glad that I stayed mostly in control.

I'm posting this to share my experience, and as a warning of sorts that even "tame"-seeming forms of meditation can have surprisingly intense effects that it's good to be prepared for.

I'm also curious if any more experienced meditators or practitioners have comments or possible explanations for this phenomenon.