This is called post-viral syndrome. That is, something bad that remains after a viral infection. People simply have no strength for anything.
It's not about lactic acid in the muscles. Everything is much more complicated and somehow tied to cytokines like interferon.
By the way, if you began to tolerate alcohol badly or smoked before, and after an illness you do not want to smoke, then this is also bad. This is a sign that there is a problem in the body. Tell your doctor about it.
What to do for prevention
If you get sick with covid, then you will have to follow these rules. Otherwise, you can become very weakened later:
Lie back. The body will have to fight a strange virus, so don't interfere with it. Just lie down and do nothing. Do not wash windows, do not dust off the cabinet. Just rest.
Resting means not straining your body and brain. That is, do not just lie on the couch, but also turn off the TV. Don't surf the Internet or use your phone. Do not swear or conflict with anyone. This puts a lot of stress on your body.
Sleep more.
Eat as usual. Even if you don't feel like eating, try to eat as usual anyway. Some people with covid have vomiting and diarrhea, but more often they simply have no appetite. To fight the virus, you need nutrients.
Drink more liquids than usual.
Disperse the blood. Several times a day you need to get out of bed and move carefully. This will accelerate the blood in the veins and reduce the risk of thrombosis.
Get ready for the fact that after the illness you will be none. Don't make plans or plan to go to work. As it turns out, you will come out.
Allow yourself some fun that doesn't take away your energy.
Stop working. If you are attacked by a virus, then give your full attention to it. Sit on sick leave.
What to do if you feel better
Start doing something around the house. Then rest again. At this time, you need to constantly check your strength. If weakness rolls in, then lie down and rest.
Try, for example, doing what you did while standing while sitting. It is easier.
Weakness can come in waves. There will be bad days and good days. Don't be intimidated by this.
Develop yourself a daily routine. Do something at the same time every day. So you can track your progress and notice a decrease in performance in time.
Start straining your brain. Do some remote work, surf the Internet, calculate your budget and all that.
Don't force anything. This leads to long-term weakness.
Do yourself something nice and have some fun every day. It helps to come alive.
Load yourself up with work gradually. But gradually.
When will it pass
If after 3 - 4 months after the illness you feel overwhelmed, then go to the doctor and let him look for some reason for your weakness. The virus could damage your lungs or heart. There may be weakness from this.
Post-viral syndrome is an incomprehensible sore and can last indefinitely.
