1- Dehydration, for example if you experience diarrhea and you are losing water from your body and at the same time you're not drinking as much, another example is sun exposure for a long time without compensating with fluid intake.
2- Blood loss, such as bleeding from the intestinal tract or internal bleeding.
3- Severe infections can sometimes lead to low blood pressure.
4- Medications: some medications are given to lower blood pressure to persons with high blood pressure ( hypertension), sometimes these medications may cause low blood pressure and require dosage adjustments, one must also pay attention to medications such as sildenafil( Viagra) which can cause low blood pressure , especially when used concomitantly with other medications that may lower blood pressure.
5- Other causes of low blood pressure may include heart problems, severe allergic reaction, and orthostatic hypotension( low blood pressure that occurs only when you stand up).