If your anxiety prompts bouts of muscle weakness, it means the body’s stress response has been activated. This can cause weak muscles in a variety of different ways. For example, when in fight-or-flight mode, our blood pressure spikes, our muscles contract, and blood gets rerouted to the organs most essential for responding to danger (via AnxietyCentre.com). As a result, this can cause feelings of muscle weakness.
If you’re someone who starts to hyperventilate when anxious, this could also be the reason your muscles feel heavy due to the drop of CO2 in your blood that occurs when your breathing accelerates. Our blood sugar can also drop if anxiety is experienced on an ongoing basis. In the long run, lightheadedness, fatigue, and muscle weakness may set in. Alternatively, because anxiety can put us in a heightened state of worry and awareness, we may be more likely to think we’re experiencing muscle weakness even in the absence of a clear cause.