Satan has many ways and means.

It is recorded in Sahih al-Bukhari that the Prophet (peace be upon him) said,
 
"During your sleep, Satan ties three knots at the back of your Decks. He breathes the following into them, 'The night is long so keep on sleeping.' If the person wakes and praises Allah, then one of the knots is unfastened. And if he performs ablution, the second knot is unfastened. When he prays, all of the knots are unfastened. After that he will be energetic and happy in the morning. Otherwise he would get up listless and grouchy."