If you are really worried about it, or any other medical condition, speak with your oncologist or GP. It really isn't worth the anxiety to "sit on it" for more than a day or so.
Now a quick search on the 'net for side effects of Herceptin indicates that it is more likely to give you a stuffy nose than a runny nose. But as all my doctors keep telling me, "everyone reacts differently".
As far as treatment, I would go for a box of tissues and, only because I'm not on any medication at the moment, a few doses of OP rum (or equivalent) - gargled - at least 4 times a day.
Speak with your doctor!!!
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