Question about LGI bleed case

Hi,
I am a nurse who works on a telly unit. We do accept medical pts if our census is low, but I do not have much experience with these cases.
I had a pt last pm that was admitted for a lower GI bleed and diarrhea. She was in her 60's, didn't have much of a med history (I think gout, smoker, and HTN). Anyway, in report I got that she was on q12 H&H, and IVF NS at 80/hr. Scheduled for a colonoscopy the next day. Bowel prep, clear liquids. Not alot of meds. Very poor appetite. Abdomen slightly distended, no pain. Weakness and dizziness. All else WNL. Vitals stable, B/P running slightly low. Any way the reporting RN told me that her H&H had dropped significantly from the night before (can't remember the exact numbers, but not critical). MD called. No orders except to continue to monitor. Did H&H at 900pm, lower than normal, but again not critical. Had had diarrhea, but no frank blood in it. At about midnight, called to room by NA, pt on toilet, some blood on bed, looked in toilet, lots of blood there and on pt. BP 105/60's pulse 131 (she's been tachy). Says shes weak and dizzy, but no more than usual. Call doc, STAT H&H, check B/P after pt gets in bed and call him w/ results. OK, B/P drops to 86/58 after pt lies down. pulse 103. H&H drpos about 2 points. Call doc, 500cc bolus and do H&H in am at 0500. Pt had 1 more apparently bloody stool, then one stool that did not appear bloody. H&H in am had risen slighltly.
My question is this: Can someone have an intermittent bleed that can cause the H&H to go up and down? What are the typical diagnoses in a pt with an on-off bleed? When I go back to work, I will see what the colo results were, but I am curious if anyone has any ideas or has seen something like this.
Thanks,
Amy