When electricity first was introduced as something that could be used in homes, many considered it strange and scary, but these days, most of us are used to having access to electricity pretty much anywhere we are located. Some even make sure they have a way to power their devices when out camping in the wild. So, being unable to trust that you have a reliable source of power in this day and age might seem farfetched for some, but there are still areas of the country where brownouts and blackouts are quite common.
If you live in such an area, there might not be much that you are able to do to remedy the situation short of getting your own supply, such as a generator or solar panels, but if you are the only one in the neighborhood that is experiencing issues, there is most likely something wrong in your home.
So, what are possible sources of electrical issues in a home? One possibility is that a circuit is overloaded. You might deduct this is the reason if the power fluctuates when a particular appliance turns on. Another could be old wiring that is decaying. If you want to find out for sure, your best bet will usually be to hire an electrician that has the experience and training to help you out.