I've noticed the same thing.  I've been meditating daily for many years and do a healing/releasing type of meditation.  I find that a castor oil pack on my stomach just plain releases foreign energy from my body - all over.  I've also learned that if I do it two, three or more days in a row, the second and following days are not as healing as the first day.  There has to be a build up in the body that that castor oil releases.  I find that the same thing happens if I apply only a small pack to my knee or leg.  Have had that happen several times.

Castor oil is also know as Palma Christa, or the Hand of Christ.  I believe it.  It has healing properties far beyond what we recognize on a body level, and I don't think that any of it penetrates the skin.