Do i need to ask my regular doctor for a refferal to see a physiatrist?

Depends on insurance: Your insurance plan may have only your pcp limit your referrals to other specialists including physiatrists. If your insurance does not limit your specialist referrals then you can self refer yourself to a physiatrist.

Usually: Most physiatrists will see patients who call without referral but many are quite busy and a referral letter will 'grease the skids' and also provide information which the physiatrist can use to enhance the quality of the visit.