Many people are azy or have episodes of laziness where they have a sense of demotivation and are not inclined to do something productive. The correct term for actual laziness is indolence.
Most people find themselves feeling lazy, or tired by the end of the day. In those cases it's just the body going through recovery both physically and mentally.
Others have a condition of indolence, they instead prefer to do nothing all day every day. They are people who suffer from laziness and many develop serious health problems such as obesity. Often, upon a closer look other things are contributing towards it. Depression, abuse and health problems could restrict a person to doing nothing every day.
In cases of serious laziness that last for weeks on end, it's best to see a professional. When you're going through this same problem all the time and the feeling doesn't seem to go away, then it's not a good sign.
If you're going through an off day, then the best thing is to motivate yourself by doing your favourite thing. Try to inspire positive thoughts that invoke some energy, such as, what are the good things that can come from this activity. Focus on the results which will help you push through.
Positive thoughts will always stimulate a positive emotion. Positive action also has the same result, such as doing exercise, calling a friend, having a good laugh or playing with your pets. They can contribute towards feelings of motivation, excitement and willingness.
Sometimes the only real effort is in making that first decision and taking the first step.