The author of this text is unknown. I grabbed some text from the internet to get a discussion started, and will refine this as we go.
It's exactly that -- an attitude you didn't intend. There are two types: (1) Nose low, increasing airspeed and (2) Nose high, decreasing airspeed.
(1) Nose Low - indicated by VVI showing a rate of descent (may be hard to read if it's pegged against the maximum rate), AS increasing and Altimeter unwinding showing a loss of altitude.
Correction Technique: Check the T&S, if it shows a turn, return to a wings level attitude. If AS is increasing, reduce power. If you are near maximum airspeed, you may need to reduce power to idle. Now bring the nose up to the horizon. This is the tough part. The VVI will give you the first indication, but it has a built-in lag. If you're not familiar with this error situation, read the "Errors in the Vertical Velocity Indicator" article on the Technical Editor page in the "General" section. The best way to use the VVI is to remember that when it reverses (in this case from a negative figure and starts up toward zero rate of climb), you are near level flight. Also use the Altimeter to see if the loss of altitude is slowing or stopped. You probably over corrected using the VVI, so check it again to watch for another reversal. Reset power to cruise setting.
Be careful not to aggravate a nose low attitude by entering what is referred to as a Death Spiral. With the nose low in a banked condition, pulling back on the yoke doesn't raise the nose. It aggravates your predicament by tightening the turn and causing more altitude loss. That's the reason rolling wings level first, is vital.
(2) Nose High - indicated by VVI showing a rate of climb (may be hard to read if it's pegged against the maximum rate), AS decreasing, and Altimeter showing an increase in altitude.
Correction Technique: Begin adding power and check the T&S. If you are wings level, roll into a small bank. If airspeed is decreasing to a dangerous point (near stall), you may need maximum power and you may need to increase your bank angle. Increasing the bank angle will help the nose drop toward the horizon since you are losing lift in the turn. As the nose nears level flight, roll the wings level and reduce power.
Above all, whichever position you find yourself in, be smooth on your recovery. If you are rough, you may well recover from the first Unusual Attitude only to find yourself in a second one. Avoid the Death Spiral (nose low) or stalling the plane (nose high).