A 28-year-old woman from Kerala presents with a 5-day history of high-grade fever, severe retro-orbital pain, myalgia, and a maculopapular rash that spares the palms and soles. On examination, she has petechiae on the soft palate and mild hepatomegaly. Laboratory findings show platelet count of 85,000/μL, haematocrit rise of 8%, and normal liver enzymes. Serum IgM dengue antibody is positive. What is the most likely clinical diagnosis?