Stiffness is there most of the time, depending on the degree of chronic low grade inflammation and/or permanent damage. Flare is when you get additional stiffness and pain, and also affects organs that are usually exempt during remission.
I am going through a flare for the past two months and the most noticeable new symptom has been fatigue and weakness. I feel sleepy most of the time, yet find it difficult to sleep and sleep does little to remove fatigue.