Is it normal for breast stimulation to cause drowsiness or relaxation?

My breasts are quite small and not any more sensitive than I imagine most others' to be, but when I touch or massage them I do find that it causes an odd (or is it?) reaction. Within a few seconds, I just get this really calm, almost sleepy feeling washing over me. It isn't like I'd pass out or anything, but it's strong enough to know it's a specific reaction, not just a relaxed feeling you'd get from feeling good in general.

It definitely only happens with my breasts, and doesn't quite feel the same as arousal, though I'll admit it contributes in a submissive sort of way. Any personal experiences or secondhand knowledge of this sort of thing happening for others?