Sometimes, either during searches or writing stories in my head, I find myself always typing in the same word: 'Hypnotized'. I'll occasionally try 'brainwashed' or 'mesmerized', but I seem to always fall back on the former.

So I was wondering, are there synonyms for 'hypnotized', or is it a narrow specified word to begin with?

Entranced is an obvious one. I can also think of enraptured, mystified, spellbound, and captivated.

The thing is, the three words that you mentioned aren't narrow. They're actually general terms. Depending on the scenario, there are many ways to describe a hypnotic experience.

A quick run through various online thesauruses will definitely help.

In the long run, you can use damn near any word for it [within reason]. It all depends on how you word it.

For example you could say something like the following
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By that point, it didn't matter what she did. Some small part of her knew that, but she didn't care. She just wanted to stay there, stay where he was. She was forever held in the palm of his hand, forever there and unable to fight him off. In a place where nothing mattered, where the only thing she could do was follow her masters commands; not that she had a problem with that.
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See? Hypnosis is obvious, but the word or any of the common synonyms are not there.

It's all a matter of wording, really. So, just get creative, and get wordy, since sometimes that's what you need to do =)

For what it's worth, I mostly search for tech-related mind control material, and boy, there are many terms.

How do I find more terms? Well, many sites have tags of some sort (boorus like this one, the bigger ones, exhentai.org, etc). Then, I search for a term like "mind_control", look at the better results, look at the tags, and find more stuff like it through those tags.