A 31 year-old pharmacist complaining of rectal pain. He describes the pain as "a severe tightness that awakens him from sleep." His bowel activity is normal. He denies rectal bleeding and seepage. He adds that sleep interruption is problematic, because with the number of hours he works, every minute of sleep is important. What is the most likely diagnosis?
A. anal abseess
B. perianal fistula
C. proctalgia fugax
D. ulcerative colitis
E. internal hemorrhoids.