The Talmud claims you are never alone. According to Berakhot 6a, the sage Abba Binyamin taught that if the human eye were granted permission to see demons, no living creature could endure the sight. They are everywhere.
Abaye put it even more vividly: demons outnumber humans, standing around us like mounds of earth surrounding a pit. Rav Huna went further with numbers—each person has a thousand demons to the left and ten thousand to the right. The proof text? (Psalms 91:7): "A thousand may fall at your side, and ten thousand at your right hand." God shields us from them, but that does not mean they are not there.
Rava catalogued the evidence of their presence in daily life. That crushing feeling in a crowded study hall? Demons. Unexplained knee pain? Demons. Clothing that wears out too fast? Friction with invisible beings. Sore feet? Also demons.
The Talmud even provides a method for detecting them. Sprinkle fine ashes around your bed at night, and in the morning you will find footprints that look like a chicken's tracks. If you want to actually see them, take the afterbirth of a firstborn black cat—itself born to a firstborn black cat—burn it, grind it, and place the ash in your eyes. But be warned: seal the remaining ash in an iron tube with an iron seal, or the demons will steal it. Rav Beivai bar Abaye tried this procedure. He saw the demons. And he was harmed. The Sages had to pray for his recovery.
The message is both terrifying and strangely comforting. The invisible world teems with hostile forces—but prayer, community, and the synagogue offer protection against them all.