Well, actually it;s low and high. When the air going over a wing that's
traveling close to supersonic is accelerated futher by the action of the
wing, it goes supersonic over the wing. When you go too fast, max mach, you
get a loss of lift. When you go too slow, you accelerate the air over the
top of wing as well due to increased angle of attack. If you load the wing
up with weight or G (same thing as far as the wing is concerned) same thing
happens. The air buffeting from the shock wave is similar to a stall ( some
sources call it a stall) and loss of control and altitude results. Recovery
can be difficult, though not impossible. There are a number of other facors
at play here, but that's the meat of it.

Pretty cool information I must say.. thanks! I guess its a whole
different world from my puny little cessna 150