Hi, Fenestil is a brand name for a medication called dimetindene, which is an antihistamine used to relieve symptoms of allergies such as itching, sneezing, and runny nose. One of the common side effects of antihistamines is drowsiness or sleepiness, and the tiredness and sleepiness you are experiencing may be related to taking the medication. It is also possible that the stomach pain you experienced after eating sushi was due to food poisoning or an infection, which could cause fatigue and lethargy as the body fights off the illness. It is important to stay hydrated and eat a balanced diet to support your immune system during this time. If your symptoms persist or worsen, it is advisable to seek medical attention to rule out any underlying conditions. In the meantime, you may want to consider taking a break from Fenestil and try other non-drowsy antihistamines or natural remedies for allergy relief. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Priyanka, General & Family Physician