One off bleeding 23 weeks

Hi mummies, I had sudden bleeding (blood trickling down my legs) for around 10mins after a hot shower. Went to gynae immediately and did a vaginal and urine test but could not find any bleeding in the vagina or urine. Gynae could not diagnose the cause of bleeding but put me on bedrest for 4 days. I have low lying placenta though at my 20 week scan. Do you all have similar experience? Very worried #1stimemom