Seeing an oral pathologist or oral surgeon is advised.
Sounds normal to me. Most people have a white coating, especially on the back, you just probably never noticed it before until you stuck your tongue out so far in the mirror.
I noticed also a white coating on the back on my tongue and two bumps on the sides. The doctor said he didn't see anything abnormal at all. As worried826 says, it seems that I didn't stick out my tongue out so far till now.
I have had a thick coating on my tongue for over 1 month now and 3 different dotors told me that they didn't know what it is. My new doctor took one look at me and said yes that a oral yeast infection and it comes from taking or mixing antibiotics which the doctors had me doing and the oral yeast infection came from that. He perscribed a medicine call nystatin 100000. The medication I didn't think did anything for me it only said to use 4 ml 4 times a day which is the equivalent of 1 teaspoon. He said to swish and spit it out. After 2 weeks I still have this oral yeast infection so I have no clue what to do or how long i should have been swishing for.