How long do palpitations last? when does it become 'too long' for normal?

Identify Palpitation: There are many types of palpitations. Some require further evaluation and or treatment and some do not. Have your doctor check to see what kind you have. Checking this is normally quick and painless.

Abnormal at 18: Palpitations at age 18 yrs usually indicates an abnormality. Diagnosis of ventricular or supraventricular arrhythmias .... Is not normal at this age. A search for the cause ... Eg. Svt or av nodal tachycardia, wolff-parkinson-white syn ..... Must be evaluated. Ventricular arrhytmias must insure no qt syndrome, hypertrophic cardiomyopathy, or channelopathies. An ECG and holter ECG needed.

Just a few seconds: I think if you need to ask how long is too long... Then something is going on. Most palpitaions are a single early beat, sort pause, then a stronger beat. I believe you are having some form of arrhythmia (abnormal heart rhythm) these are not always dangerous, but ignoring them can lead to problems. Again, i'd recommend a visit to a pediatric cardiologist or an adult structural cardiologist.

Varies: A sense of irregularity or jumping is often a disconcerting feeling but unless associated with exertion or other signs - rarely serious. Palpitations may last for minutes at a time and come in episodes which bother individuals for years. Individual flip flops can sometimes be perceived as long runs even though they are isolated. Sounds like you need a 24-72 hour monitor to figure this out.