Just to be sure, I put some of my latest batch on my lips and tongue and I can see how one might feel like the tingling, especially on the tongue and roof of the mouth, might be numbness.
I really have no idea how long the "soup" might last in the fridge - I would not even think of making it without using a preservative such as vodka or vinegar. Actually, I use a combination of colloidal silver and vodka or vinegar so that I don't have to dilute it 50/50 with preservative.
The most accurate way to measure the potency of the extract called "oleander soup" is by using a hydrometer or very sensitive weight scale. The resultant extract should have a specific gravity, or weight, of 1.07 compared to 1.0 for water alone.