Actually, even 1 rpm is is enough to cause noticeable discomfort, purely from effects to your inner ear.  In steady state, when you're rotating, all of you is rotating, including the fluid in your inner ear. The fluid is not moving relative to your body position. If you simply tilt your head, the fluid in your inner ear will keep rotating in the same direction due to its angular momentum, no longer stationary with respect to your body. Your vestibular system will interpret this 
 as new rotation and shift in balance. This can cause nausea and loss of balance, especially since your body's signals will disagree with what your visual cues are. 
 
According to NASA,  a rotation rate or 0.1 rpm or less would be required for a comfortable environment. This would give you a radius of about 55 miles for your space station.