Side effects - Short of breath after smoking DMT

[Synesthesiac]

Does anyone else experince this? SWIM has found that after whipping a bong of dmt smoke its slightly hard to breathe for a minute or so, not seriously so, but it just leaves you short of breath for a while. It could be either down to a not pure enough product, the method of smoking, or something else, but every time SWIM and his friends have smoked it this happens every time.

SWIM was using a straight to base method, without a wash, and using freeze precipation, which left sparkling clear white crystals. Due to this SWIM thought it was a nice and pure end product. He used this tek: http://www.dmt.20m.com/

Any ideas how this side effect can be avoided?