'Britney received some anonymous death threats over the phone and in the mail, and her worst fear is a kidnap plot against Sean or Jayden,' a source revealed to celebrity magazine Look.

'She's been having terrible nightmares ever since then and she wakes up in the middle of the night crying out for her boys.

'She told her head of security and he thinks it's a lone stalker.

'Her paranoia has reached fever pitch and she's wracked with fear.' -- REUTERS