You cannot roll the HSA funds over into an IRA. They will stay in the HSA or be rolled into another HSA. HSAs allow you to reimburse yourself provided the funds are used for a medical expense that has occurred after the IRA was opened. What qualifies for a medical expense usually depends on the definition presented by the IRS in Publication 502.
Being on social security usually makes health insurance qualify as a medical expense, making it likely that you will be able to receive a reimbursement. For more information on what qualifies as a medical expense, please visit http://www.ilhealthagents.com/hsa/qualified-expenses/ .