This potentially shows some huge red flags! what's the onset pattern? frequency/severity of symptoms? other symptoms? etc.
As well as the other advice already listed, ask about continence too (either loss of or difficulties). Personally i'd do a basic neuro exam for documentation and inclusion in a specilist referral letter but i would definitely refer for medical assessment to clear the really nasty stuff (ie. refer back to the GP for referral to a neurologist if needed).
As physios we have good ability to examine the Msk system and neuro function but it's not our place to diagnose UMN lesions, or major pathology without specialist investigation and advice. Appropriate "special questions" should highlight red flags to you which warrant further investigation and clearing before physio should go ahead. if it turns out to be nothing sinister then physio might be a great pathway in the end.