I was diagnosed with ms in october of 2013. with this lhermitt's sign, should i be concerned? is this a sign of a relapse? or just let it pass?

You left out stuff: So what you left out was (?): You had symptoms, you saw a doctor (neurologist?), your neurologic exam was abnormal, you had a brain MRI, it was positive for MS. You were started on DMT. NOW, you're experiencing Lhermitte's phenomenon. This is new. - Lhermitte's suggests lesion(s) in the cervical cord. You may need to have (or repeat) an MRI of your cervical spine. Discuss with your neurologist.

Lerhmitte's: Sometimes the symptoms of Lerhmitte's will pass over time, like a lot of other MS symptoms. It helps to have proper treatment and follow up, including vitamin D, something to prevent MS attacks, and watching out for secondary symptoms.

Get evaluated: If you have been stable for months and recently began experiencing Lhermitte's, and it has lasted longer than 24 hrs, this is indeed a relapse. How it gets managed could be variable, and your doctor needs to assess. Would suggest you always inform your doctor of changes, as successful MS management involves attention to even minor details. Best of luck.