Place the senna pods in a glass bowl and pour over the boiling water. Let steep for about 30 minutes, and then strain through a sieve or a piece of muslin into a blender. Add the sugar and figs to the senna infusion and whizz until smooth. Pour into a saucepan and heat slowly to reduce, stirring occasionally, about 25 minutes. You want to end up with a thick, glossy sugar-like syrup. Add the lemon juice and stir well, and then remove from the heat and pour into a sterilized 150-milliliter bottle. Shake well before use. Take 2 teaspoons before bed when needed. Don't use for more than a few days at a time, or if you have severe abdominal pain. The syrup can be stored in the refrigerator for 3 to 4 weeks.