The greatest danger is in using beta blockers without the supervision of a competent physician or in not following your physicians guidelines when taking these kinds of medication.  There can be a number of negative side effects associated with taking beta blockers, nearly all of which are explained at http://betablockerssideeffects.com

Here are three of the possible side effects of using beta blockers.  Anybody taking beta blockers as medication and experiencing any of these side effects should immediately report them to their health care provider.

One common (and dangerous) side effect is fainting or lightheadedness due to abnormally low blood pressure. This is referred to in scientific terms as hypotension. It's the extreme inverse of the symptoms that cause most people to start taking beta blockers in the first place.

A second possible side effect is the feeling of minor or chronic chest pain. Since beta blockers have strong effects on the circulatory system, this can never be a sign that everything is 'just fine' and the patient should cease use of the medications immediately and contact his or her cardiologist.

Thirdly, people could experience the kind of allergic reactions that can accompany just about any medication. These include symptoms such as getting a rash with no explanation, hives, itching, swelling, wheezing, breathing difficulties, or even a tough time swallowing food.

You may or may not experience any of these side effects when using beta blockers.  Maybe the side effect that you get is not related to beta blockers and related to something else. Do not, however, fail to consult the physician who prescribed them to you before continuing use of the medication.