Open Question: When medication leaflets mention Possible and rare side effects, how rare is possible and how rare is rare?

Mine said: Possible side effects: drowsiness (I have been provided for the purpose, this drug), headache, muscle incoordination, and dry mouth, blurred vision, urinary difficulties, and stomach upset. Rare side effects: insomnia, nervousness, high fever, shivering tremor and epilepsy type convlusions. I have anxiety, so give chlorpheniramine tablets to help me sleep but I am worried about blurred vision, and even more tension and convlusions! Thanks in advance inches