I believe the newer trackpads use one of Apple's haptic motors to provide the click feedback. They are a linear motor and there is the possibility that the driven element that shakes the trackpad could get stuck. It might be worthwhile to firmly tap the trackpad a couple of times on each edge on a hard surface to see if that would free it up again. I'm not sure which direction the motor is oriented in, horizontally across the width the of the trackpad or vertically across the top to bottom.
The only problem with this solution is that if it did get stuck once, then whatever caused it to stick originally will likely happen again.
thats worked for you though?