1.'Goodbye' from the eponymous album 'Slipknot (1999)' speaks of feeling "The noose grows tighter... the pain, unbearable. As they slip away, slip away..." This expresses a sense of losing hold and fading into nothingness.
2.'Left Behind' also from 'Slipknot (1999)' conveys the sentiment of being "Left behind, I have left behind. Forgotten faces I have left behind". It captures the experience of slipping away while being forgotten and left behind.
3.'Surfacing' from Slipknot's sophomore album 'Iowa (2001)' contains lines such as "Drowning beneath you're pulling me. Drowning... drowning deeper than you think.." where vocalist Corey Taylor sings about an inability to stay afloat and feeling dragged downwards, suggesting slipping away into uncertainty.