Voluntary fasting

Have a question on fasting. Ultimately I plan to take this question to God for an answer, but thought I might ask to get more information and ideas to ponder on first.

So, I had a doctor's appointment today and was asked to fast for 8 hours before. I decided to turn it into a spiritual fast as well because "might as well" gain that extra power from a fast since I'm having to fast anyways. I remember a leader talk with this same sentiment when I was a youth.

When my wife heard I was doing a spiritual fast too, she said that wasn't good. That we are taught to "voluntary fast", and if I'm needing to fast for a medical reason, then the spiritual fast is not voluntary. I had never thought about it like this before.

I'm not sure what to think on the topic now. I can see it from both perspectives. I don't believe it's "bad" to fast alongside a medical fast, but I can see how it could be more powerful if the fast is a set aside thing for the sole purpose of it being a spiritual fast.

Just wanting to know true principles and do things the way God would have me. Any perspective, insights, and knowledge would be appreciated. Thanks