Causes
The current knowledge of the neural pathways responsible for the perception of the heartbeat is not clearly elucidated. It has been hypothesized that these pathways include different structures located both at the intra-cardiac and extra-cardiac level. Palpitations are a widely diffused complaint and particularly in subjects affected by structural heart disease. The list of etiologies of palpitations is long, and in some cases, the etiology is unable to be determined. In one study reporting the etiology of palpitations, 43% were found to be of cardiac etiology, 31% of psychiatric etiology and approximately 10% were classified as miscellaneous (medication induced, thyrotoxicosis, caffeine, cocaine, anemia, amphetamine, mastocytosis).The cardiac etiologies of palpitations are the most life-threatening and include ventricular sources (premature ventricular contractions (PVC), ventricular tachycardia and ventricular fibrillation), atrial sources (atrial fibrillation, atrial flutter) high output states (anemia, AV fistula, Pagets disease of bone or pregnancy), structural abnormalities (congenital heart disease, cardiomegaly, aortic aneurysm, or acute left ventricular failure), and miscellaneous sources (postural orthostatic tachycardia syndrome abbreviated as POTS, Brugada syndrome, and sinus tachycardia).Palpitation can be attributed to one of four main causes:

Extra-cardiac stimulation of the sympathetic nervous system (inappropriate stimulation of the sympathetic and parasympathetic, particularly the vagus nerve, (which innervates the heart), can be caused by anxiety and stress due to acute or chronic elevations in glucocorticoids and catecholamines.
Codeine/paracetamol, also known as codeine/acetaminophen and co-codamol, is a compound analgesic consisting of a combination of codeine phosphate and paracetamol (acetaminophen). Codeine/paracetamol is used for the relief of mild to moderate pain when paracetamol or non-steroidal anti-inflammatory drug (NSAIDs) such as ibuprofen, aspirin or naproxen alone do not sufficiently relieve symptoms.In 2019, it was the 173rd most commonly prescribed medication in the United States, with more than 3 million prescriptions. Combination products containing codeine are available over the counter in Barbados, United Kingdom, Israel and Costa Rica. Of the European Union (EU) member states, 12 countries (Bulgaria, Cyprus, Denmark, Estonia, France, Ireland, Latvia, Lithuania, Malta, Poland, Romania, Slovenia) allow the sale of OTC codeine solid dosage forms. Side effects
The most common side effects of co-codamol are constipation and feeling sick (nausea) or sleepy. Other side effects may include blood from mouth, skin rashes, dizziness, sedation, shortness of breath, hypersensitivity reaction, fainting (syncope or near syncope), confusion, loss of short-term memory, changes in blood, allergic reactions, euphoria, dysphoria, abdominal pain, itchiness, easy bruising, bleeding gums, vivid dreams, dry mouth and addiction.Genetic differences between people give rise to differing rates of metabolism of codeine to morphine. In about 5% of people this may happen particularly fast, leading to higher levels of morphine being passed through breast milk in amounts potentially able to cause fatal respiratory depression of a breastfed baby. References
External links
"Acetaminophen mixture with codeine phosphate". Drug Information Portal. U.S. National Library of Medicine.