Hello,
Thank you for your query at DoctorSpring.com
Sometimes over straining while constipated, can lead to such loss of consciousness because there is peripheral pooling of blood, leading to momentary lack of blood supply to brain. However, it does not lead to any long term damage.
Since she fell down and hit her head and it was followed by vomiting, she should get a CT SCAN done to rule out any minor bleeds.
Also her stool needs to be tested, because black stool indicates hemorrhage and could be due to colitis, long term ulcers, or due to damage to the rectal mucosa.
Meanwhile you can give her Syp. Lactulose 20 ml once before sleeping, which will help in clearing the bowel. And Cap. Omeprazole 20 mg, once before breakfast for 7 days will help in preventing any further bleeding in stool.
Feel free to discuss further,
Regards.