The only time when the verb "necesitar" is reflexive is when you mean that you need yourself, for whatever reason you want to make such an emphasis.
- Yo me necesito (a mí mismo).
Maybe you intend to emphasize that you don't need anyone else.
It is incorrect to say "yo me necesito unos zapatos" (I need me some shoes.)
I'm trying to figure out why you have this question to explain better. If you need more explanations or examples, let me know.
