A reader asked the question about Tulsi and fertility because he was a younger person and once CFS is in remission, wants to have a family. Most CFSers are post family-additions, so this post is focused on the younger ones only. This also appears to apply to Chinese hibiscus.
The PubMed article that raised his concerns was: “Effect of tulsi (Ocimum Sanctum Linn.) on sperm count and reproductive hormones in male albino rabbits” which states: “present study clearly show that tulsi treatment (2 g/day) brings about a reduction in sperm count [on rabbits]” and later “This contraceptive effect was comparable to female contraceptive pills, and was reversible.” on the mechanism that they suspect was occurring.
Benzene extract of O. sanctum L. leaves have a reversible anti-fertility effect, as O. sanctum L. extract (250 mg/kg body weight) for 48 days decreases the total sperm count, sperm motility and forward velocity. The percentage of abnormal sperm increased in caudal epididymal fluid and the fructose content decreased in the caudal plasma of the epididymis and the seminal vesicles. All these parameters returned to normal two week after the withdrawal of the treatment.” 
So there is no real concern about starting a family later!