A sudden increase in your energy bill can be caused by several factors. Common reasons include inefficient HVAC systems, such as dirty filters or malfunctioning components, leading to increased energy usage. Seasonal changes, like extreme heat or cold, can also drive up usage. Additionally, new appliances, increased household activity, or issues like poor insulation and air leaks can contribute. It's advisable to inspect your home for these issues and consider a professional energy audit to identify and address specific problems.