If you're loaded down with more than you can handle, you're overburdened. Whether you're overburdened with difficult work on your beet farm or overburdened with worry about your sick cat, it's just too much.
Being overburdened means having far more burdens than you are physically or mentally equipped to deal with. These can be heavy loads, duties, worries, or responsibilities. If you're overburdened with backpacks and food supplies on a trek through the desert, you may collapse from exhaustion. And if you're overburdened with math homework, you might stay up all night desperately trying to finish. Either way, it's too much for one person to handle.