Can Oxymetazoline Hydrochloride addiction cause blood urination or weakened immune system leading to UTI?
No way nasal spray would cause blood in the urine. The problem you are having is well known with nasal sprays. It called rebound stuffiness and the only way to get over it is to stop using nasal sprays. Oral decongestants will help some during this withdrawal. Anytime there is blood in the urine it is serious and medical attention should be found.
