questions to Swamiji on phyical symptoms

Swami ji,
I've noticed - at least thrice in the last 5 years - that when my mind becomes very very calm (when reading on spiritual matters, I'll elaborate shortly), I show these these symptoms:
(1) my breathing becomes very infrequest (very slow)
(2) my breathing becomes very shallow (air taken in/out is very small in amount)
(3) I feel sleepy, sometimes end up sleeping or sometimes body becomes calm as sleeping but mind is calm & conscious.

The occassions it happened was
(1) reading "Autobiography of a Yogi" by Paramahansa Yogananda and thinking about it
(2) reading (on http://www.cosmicharmony.com or similar websites) that God's creation is teeming with intelligent advanced higher life forms, and thinking of the blissful spiritual kingdom (where probably one day humanity will land up after evolving spiritually) that exists beyond our current perception, and the one-ness of the creation with the Almighty.

I'm a 34 year old Hindu, generally healthy (except with a recent liver problem). Are the symptoms I describe above ok/normal/common?

Regards,
Rajib

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