Sound's like a poorman's "Speedball", except your not injecting. I personally haven't done this combo, so if I were to give you any advice it would be to be careful and be prepared your body potentially being very uncomfortable. I know that other depressant/stimulant combos are often very pleasureable experiences, but bear in mind you are sending the body 2 totally opposite sets of signals. On the flip side of the coin, if you look at the procedures for treating a benzo overdose - treating the victim with a strong stimulant is quite often listed.
Keep us posted, I'm curious to hear what your experience is like.
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"I dislike the drug you are using, but I would defend with my life your right to use it."
- Paraphrase on Voltaire
"He who makes a beast of himself gets rid of the pain of being a man."
- Dr. Johnson
"We do not sense imagination enough to sense what we are missing."
-Jean Toomer