You did not wire up the voltage source correctly. The negative terminal of the voltage source should be connected to ground, not to OUT.

You did not wire up the voltage source correctly. The negative terminal of the voltage source should be connected to ground, not to OUT.

Here is the circuit with the +5V node replaced by a voltage source V2, and closer to the layout of your circuits.

^{simulate this circuit – Schematic created using CircuitLab}

With the parameters for SW1 set at V_T = 2.5 and V_H = 1.5, the output looks like this:

In the edited version of the question, there is a circuit similar to this, but with the parameters for the switch set at Vt = 2.5 and Vh = -0.75. Try changing Vh to 1.5 as in the original circuit.