The person may become much sleepier.
The person is likely to spend more time sleeping, and will often be drowsy even when they are awake. They may also drift in and out of consciousness.
Some people become completely unconscious for a period of time before they die - this could be short, or as long as several days.
It is normal for a dying person to sleep more. They may generally become less interested in what is going on around them, and have less energy to take part, but this does not necessarily mean they are no longer hearing what you say to them.
It is important to remember that, even when the person is or appears to be sleeping or resting, they may still be able to hear you.
Do not feel that you need to stop communicating with the person. You might want to carry on speaking quietly and calmly to them. You could also try letting them know you are there in other ways. For instance: holding their hand, reading to them, or playing their favourite music.