Intubation is a procedure where a plastic tube is slipped into the trachea, down a ways, and a cuff is inflated to maintain a patent airway. It is a harmless procedure, the biggest complication being chipping a tooth from the blade used to guide the tube. In many cities paramedics are trained in this procedure and can perform it on the street. In the case of a serious asthmatic attack it enables the patient to be "force fed" air to open up the most congested and restricted passageways. There are no afteraffects from being intubated. One a tube is in place it is "slightly uncomfortable", but not intolerable. There is no pain associated with the procedure. When an asthmatic patient comes into an ER there is often discussion of intubation. It does not necessarily mean they were seriously considering intubating you. One of the reasons is that in many hospitals only anaesthesiologists are authorized to perform the procedure. The nurses and physicians in the ER are restricted from doing so. Since an anaesthesiologist is often not available a paramedic is sometimes grabbed from an ambulance pulling in to perform the procedure. And the anaesthesiologist presents the bill, of course. Timely use of emergenmcy medications will usually (but not always) preclude the need for intubation, but if it is necessary, it is not a procedure that is painful or has long-lasting problems. When you do a lot of intubations you get better at it. The biggest problem is that there are two passageways, the trachea leading to the lung, and the esophagus, leading to the stomach. It is possible to stick the tube down the wrong hole. That is why the valecula must be visualized and the lung fields ausculated immediately after the procedure.
Asthma can be life threatening.
Yes it is, some people get to the point of not being able to breathe at all so you have to manually breathe for them (intubate) or die from lack of oxygen.