is Autofellatio Safe on the Spine & Internal Organs?

My question is it's safe to do the practice of felating myself with my mouth? i found out at 16 that i can do it if i get into correct position. i'm not gay and as long as it's a solo private practice with no harm i would like to continue.
it's not very gentle on my body especially on my spine and neck as i need to warm up and stretch for at least 30 minutes to get the reach as my penis is only  about 6.5 inches long, and after all is done my back and neck feel very sore for the next two and three days at the beginning but now it's only like that for the next day. i'm also concerned at my internal organs as it feels sometimes that am putting too much pressure on them especially as it seems that my upper back is the one doing most of the bending and i feel like the rib cage is causing most of the pressure because of it's solidity and the way it extends down the frontal body.
one more thing is that it also causes my throat to be soar for the next day or two.

i didn't dare to ask a doctor face to face so please give me as thorough answer as possible.

Thank you,

[automan]

I do it myself, and am now 40.  I think as long as you stretch (as you say you do), and don't force your body into extreme positions it isn't ready for, you are OK.  
If you do it regularly and for long periods of time, it can cause your neck to straighten and lead to permanent neck damage.
I suggest that for every hour you do it, you spend an hour doing neck curvature exercises (e.g. roll up a towel to put under your neck, lie on the floor on your back, and put your legs up on a bed or sofa).
This should counterbalance the pressure and stress forcing your neck to straighten.
Be careful, and enjoy ,