A month seems too soon for the haemoglobin to drop again, but I suppose it depends on the cause. For me an iron transfusion would usually last a few months. What you are describing actually sounds more like low blood pressure, apart from the sleeping 18 hours bit: dizziness, and feeling faint when standing up quickly. Second having another blood test done. And get a blood pressure test while you're there.
Dx Crohn's in summer of 2000. (Yay )
Tried and failed: 5-ASAs, azathioprine, 6MP, Remicade, methotrexate, Humira, various diets.
Had surgery Feb '13 - subtotal colectomy with end ileostomy. First thing to put me into remission in 13 years.
Had second surgery 10th July '15 to reverse the stoma and connect the ileum to the rectum. Feeling rough.