This can be different for each person. A mild flare for me feels like the flu with a little fatigue. More severe flares feel like the flu with fatigue and joint pain and the worst flares I have feel like the flu with joint pain, swelling and excruciating all over body aches. I get other symptoms that will be situational as well: heartburn, gastrointestinal distress, headaches, dizziness, aural migraines, sore throat, skin rashes. I have mild pain constantly and brain fog.