When I'm flaring I get night sweats badly - nothing worse than waking up in the middle of the night freezing cold, soaked like someones thrown a bucket of water over me and absolutely stinking! (One advantage of having a double bed to myself though - I just switch sides to the 'dry side' and change sheets in the morning, when I had a single bed hell I'd just head straight to the sofa rather than have the duvet change struggle in the middle of the night!)
Night sweats aren't pleasant and can often be a sign of something dodgy going on, it can be down to something as simple as a side effect (such as from steroids) but it can also mean your bodys trying to get rid of something like an infection or theres inflammation there. Personally, I get night sweats if I ever have to have a dose of steroids (rarely do as they don't sit well with me) or if I'm in a flare or about to flare. It might be worth having some bloodwork done to check for infection or inflammation, you lose a lot of fluid in a night sweat so make sure you drink plenty of water after to rehydrate and maybe add an electrolyte solution like Dioralyte (thats the UK name, I think its something like Pedialyte in the US I'm not sure)