No. You can do-it-yourself. Once you know what to look for, you can seal air leaks all around your home on your own. When everything is sealed, adding insulation to your attic will make you home more comfortable.
On the other hand, hiring a home energy-efficiency expert can be a good thing. Contractors have experience along with tools and instruments they can use to find problems areas quickly. They know the proper materials to seal leaks and can add insulation efficiently.
Visit Seal and Insulate with ENERGY STAR for more details. Look for the Do-It-Yourself (DIY) Seal and Insulate Guide for help.