For years I've had the habit of making tiny adjustments to my sitting posture every few minutes during meditation: relaxing my hips a little more or correcting a feeling of slumping by pulling the upper spine up straighter. I noticed a quote of the day on this site in which swami Sivananda advises keeping perfectly still for three hours at a time. Inspired by his advice, I decided to be more strict with myself about holding a steady posture and not making frequent adjustments. I found it much easier to stay focused mentally when sitting in is way.
But about forty five or fifty minutes in to each meditation session I start feeling a bit cold, although the temperature in my room is quite warm. I set a timer for an hour and if I sit still like that until the hour is up, as I unfold my legs from lotus posture at the end of the session, the cold chill becomes momentarily so strong that it resembles the feeling of having a fever. That lasts only a few minutes after the end of the session so I wrap myself in a blanket and then I warm back up.
I suspect what is happening is simply that blood isn't circulating well through my legs so they gradually cool down while I sit. When I unfold my legs, the blood flow is restored all that cold blood from the legs circulates around and cools the upper body. It takes a few minutes for everything to heat up again.
So here's my question: I've been feeling sick with common cold symptoms since the second day I tried sitting more still during meditation. Should I just keep working at it gently and hope that my body will adjust or am I doing something wrong that needs to change to avoid causing health problems?