This sounds quite serious, and I strongly recommend that you get in to see your primary care doctor
for a complete evaluation as soon as you possibly can. The list of symptoms you mention is pretty broad, so it is hard to narrow things down much in this answer. Therefore a good, thorough medical evaluation by someone who knows you well is the way to go.
The combination of dizziness
and weakness could have potentially serious medical causes. For example, a stroke or multiple transient ischemic attacks (sort of like "pre strokes") could easily cause these symptoms and would need to be identified and treated as quickly as possible.
The fatigue and sleepiness could be caused by an imbalance in the thyroid gland, and the muscle heaviness could be caused by any number of imbalances in the electrolytes in your blood stream. If you have recently started any new medications, one of those might be the culprit as well.
Your doctor will start by taking a full history and performing a detailed examination. Then, they will almost certainly want to perform some blood work as a way of searching for a cause. Based on what they find, they'll be able to give you more concrete advice. Again, please see your doctor as soon as possible.