Is it safe to drink those laxative teas with senna in them on a daily basis?

Better not too. Just because it's natural doesn't mean it's safe (hemlock killed socrates). Chronic stimulant laxatives: senna, cascara, aloe, triphala (natural), can lead to dependency, affect the nerve supply of the bowel. Better: fiber foods (better than supplement), fluids, activity. Occasional stimulants: figs, prunes, senna etc.Ok. Why constipated? Meds, diet, thyroid, metab, anatomy. Other lax available.
No. While it probably would be ok to take senna 7 days straight. Senna does have toxicities which one should be aware of. Senna is not recommend for patients with cardiac problems or inflammatory bowel disease. Senna toxicity could cause kidney or liver problems.