Proper way to give metta

Is it necessary to only feel subtle sensations while giving metta or is it only required to be equanimous while giving metta. I have sometimes felt painful sensations that cannot be 'shaken away' after a sit and find it harder to concentrate on giving metta. So should one only be equanimous and carry on with the practice or leave metta bhavana to another time? What works for you while radiating metta?