It was always at night -- the arrests invariably happened at night. The sudden jerk out of sleep, the rough hand shaking your shoulder, the lights glaring in your eyes, the ring of hard faces round the bed. In the vast majority of cases there was no trial, no report of the arrest. People simply disappeared, always during the night. Your name was removed from the registers, every record of everything you had ever done was wiped out, your one-time existence was denied and then forgotten. You were abolished, annihilated: vaporized was the usual word.
Arrests happened at night. People were removed from their homes, they felt interrogated by a bright light which was surrounded by a great group of people (the reader assumes these are the Thought Police). After being taken out of bed, a criminal had no rights to trial. No miranda rights were offered. Although it does not directly state that criminals were killed, they must have been because their existence was completely erased from society.
At this point in chapter 1, Winston is fearing the worst because he just completed a thought crime. He knew it was only a matter of time before he would undergo the process of arrest suggested by the words above.