The 32-year-old defendant, who cannot be identified, is accused of carrying out the sexual assault at their home in the early hours of Sunday morning.
His lawyer said he emphatically denies the alleged offence.
Belfast Magistrates’ Court heard the man claims he went into his mother’s bedroom to get cigarettes.
According to his account she woke up when he lifted a bed sheet to look for a lighter which had fallen from the packet.
Defence solicitor Feargal MacElhatton told the court: “She said ‘You’re trying to have sex with your mother’, which he denied by saying ‘catch yourself on’ or words even more emphatic than that.”
The man left their home a short time later and contacted a relative to say ‘My mother’s at it again, she’s gone crazy’, Mr MacElhatton submitted.
He stressed that the accused maintained his denials throughout five interviews, and also provided intimate samples for forensic tests.
Opposing bail, a detective cited the vulnerability of the alleged victim.
“She has a range of disabilities,” the detective said.
Concerns were also raised for the accused’s own safety.
Deputy District Judge Trevor Browne was told police have notified the man about a potential threat to him believed to come from other family members.
Granting bail, however, Mr Browne banned the defendant from any contact with his mother.
He is only to be released when an address approved by police is identified and confirmed.
The man is due back in court in four weeks time.