Susan Misiewicz, from Cotgrave, had a hysterectomy on the NHS, at the private Nottingham Woodthorpe Hospital.
The swab was left inside her during a second operation to stop internal bleeding hours later in July 2009.
The hospital said it had referred the matter to its solicitors and was working to resolve the claim.
Mrs Misiewicz said she did not know what the problem was, but felt unwell for weeks after the operation.
“I was in continual pain, absolutely shattered. It was a nightmare and I just didn’t want to get out of bed in a morning,” she said.
She said the NHS had given the choice of having the operation at a private hospital.
“I chose the Nottingham Woodthorpe Hospital, mainly because I could get it done quicker there and out of the way,” she said.
A spokesperson for NHS Nottinghamshire County said: “We will investigate all incidents with the relevant organisations and ensure the appropriate actions are taken.”
Julie Hardy, Mrs Misiewicz’s solicitor, said: “Determining who was responsible depends upon the nature of the contract between the NHS and the private hospital.
“At the moment those contracts haven’t been disclosed and neither party has accepted that they bear responsibility for what happened.”
The swab was spotted in a scan at Woodthorpe, which is run by Ramsay Health, and removed in November 2009.