I began having sleep problems around the time I was diagnosed with Stage 0 DCIS breast cancer. I'm not saying that there is a connection between the two. But my sleep problem continued for several months after surgery and radiation therapy. I reported the sleep problem to my PCP. Can't say if there was a cause and effect. The sleep problem may have been a pre-existing condition. My PCP referred me to a neurologist who had me go through a sleep study. I was diagnosed with mild OSA and placed on CPAP.
