Hi, welcome to the forum, yes, boric acid being noxious agent can cause nasal bleeding. This is mainly due to destruction of the nasal lining and septum. Eventually blood vessels get exposed and start to bleed.
Nose bleeding can also be seen due to hereditary, dry nose, lower vit k levels, some foreign body, superficial veins, rhinitis secondary to deviated septum (seems to be relevant) etc. Sometime veins are superficial and any minor harm to nose causes bleeding.
When nose start bleeding you need to sit rather than sleep, as sleeping causes increase in pressure inside head and cause more bleeding also pinch the lower smooth area of nose to prevent more blood loss. Take care and regards.
I guess I am wondering if you have a cold or did you have a cold? Is it because of dry air? Nose bleeds (depending on how often and how bad) can mean other things. How bad is your nose bleeding and how often? Sometimes you have to have a little capillary burned (sounds bad but it's not!) to stop the bleeding.