There are hundreds of causes for syncope or black out. Again, there are black outs and there are black outs. Is the patient breathing?, does the patient have a pulse?, is the pulse rapid or irregular?, is there a measurable BP?, is there any evidence of trauma?, is he/she conscious and oriented?, and so on and so forth. In most cases the causes for syncope can be found in the ER, in some cases they cannot. Asthma can make things worse. Simple cases can be caused just by dehydration and can be dealt with by giving IV fluids in an outpatient basis. It is not clear why he should have been hospitalized for several days given the three conditions mentioned: dehydration, asthma, and syncope. There is nothing else I can say without a diagnosis or a statement of what they found.