Same exact thing happened to my 58 year old husband. He was pale and very tired. Passed out at work and finally went to his doctor who did blood work. His hgb was down to 4.6 and he was hospitalized and received 4 units of blood and iron infusion. He was scoped up & down and had a small bowel follow through with nothing showing any source of bleed. A friend told me they heard about someone who had this happen after a Covid vaccine and suggested I look on line. I feel this is too similar to be a coincidence. He never had issues with his blood work prior to this event. He now is on iron supplement and has a complete blood count every 3 months since he stabilized.