Hello,
I understand your concern.
Tampons are safe but not more than sanitary napkins.
You may use tampons during day, but at night while sleeping it's necessary to use sanitary napkins.
Tampons should be changed after every 4-5 hours, if it remains there it may cause bacterial infection which may result in septicemia.
Health Tips
To avoid shock like syndrome, you should change tampons every 4-5 hours in cases of heavy bleeding, change it after 3-4 hours.
At night, use sanitary napkins.
Stay positive and healthy.