Hi Julsie,
This is nothing more than an educated guess....but I suppose it could be caused indirectly from the sjogrens. The disease causes dry mucous membranes (including the nose). Add in damage to the tissues from a cold virus and the extra strain from nose blowing, and it is logical that the delicate tissues could be traumatised enough to bleed. Overnight if your nose was slowly bleeding you could well sleep through it and the blood could pool to form a clot, which when you get up then comes out....
Hopefully it will clear up quickly for you. Have you had further bleeding during today?
If it gets worse, you'd probably better see your GP in case it is something more complicated.
Best wishes,
X C X