The components of your laptop generate heat (mainly the CPU and video chip) which must be dissipated to operate efficiently. If either is too hot, it will slow down as not to overheat.
Most laptops are designed to take air in from the bottom and blow the hot air out the side. It is best to use your laptop on a clean, hard surface like a desk. When a laptop is left on the bed or the couch, it acts like a vacuum cleaner, sucking up any dust and trapping it inside your computer. Eventually, this may completely block the exhaust vent.
You may notice your laptop fans running at full speed all the time. Prolonged use in this state can cause your laptop to overheat, damaging components or causing premature failure of the fan.
Bring your laptop to us and we will disassemble your laptop and clean it of dust and replace the thermal paste between the heatsink and the CPU & GPU. Your computer will be running cooler, faster and quieter in no time.