Thanks for using forum on HCM.
Of course your concern about appendicitis
is justified considering the symptoms you described. Appendicitis presents with pain in the right side of abdomen, vomiting
, lethargic and specially in a child where he/she cannot sit up or walk. You should consider visiting the ER as soon as you can, since appendicitis presents with more complications in children. A viral infection of gastrointestinal tract can also present with similar symptoms, however its always better for a second opinion
Feel free for further queries.