Compared to time kept on earth, there is a physical slowing of time when you travel at
a. everyday low speeds.
b. relativistic speeds.
c. both a and b
d. none of the above

If the distance between you and another person is changing,
(you are in motion relative to each other, and it doesn't matter
how fast), and you both have clocks, then ...

-- you will say that your clock and your heartbeat are running normally
but his his clock and heartbeat are running slow;

-- he will say that his clock and his heartbeat are running normally
but your clock and heartbeat are running slow.

You'll both be correct.