I'm trying to figure out how to read the state/value of a slider switch that will react when moved

I've created a sliding switch that will hide or display parts of a large form. The HTML has the following code:

<fieldset class="group">
            <legend>
                <h1>Form Type</h1>
            </legend>
            <label class="switch switch-left-right">
                <input class="switch-input" type="checkbox" id="formSwitch">
                <span  class="switch-label" data-on="Progress" data-off="Diagnostic"></span>
                <span class="switch-handle"></span>
            </label>
        </fieldset>

The CSS behind it is the following:

.switch {
    position: relative;
    display: block;
    vertical-align: top;
    width: 100px;
    height: 30px;
    padding: 3px;
    margin: 0 10px 10px 0;
    background: linear-gradient(to bottom, #eeeeee, #FFFFFF 25px);
    background-image: -webkit-linear-gradient(top, #eeeeee, #FFFFFF 25px);
    border-radius: 18px;
    box-shadow: inset 0 -1px white, inset 0 1px 1px rgba(0, 0, 0, 0.05);
    cursor: pointer;
    box-sizing:content-box;
}
.switch-input {
    position: absolute;
    top: 0;
    left: 0;
    opacity: 0;
    box-sizing:content-box;
}
.switch-label {
    position: relative;
    display: block;
    height: inherit;
    font-size: 10px;
    text-transform: uppercase;
    background: #eceeef;
    border-radius: inherit;
    box-shadow: inset 0 1px 2px rgba(0, 0, 0, 0.12), inset 0 0 2px rgba(0, 0, 0, 0.15);
    box-sizing:content-box;
}
.switch-label:before, .switch-label:after {
    position: absolute;
    top: 50%;
    margin-top: -.5em;
    line-height: 1;
    -webkit-transition: inherit;
    -moz-transition: inherit;
    -o-transition: inherit;
    transition: inherit;
    box-sizing:content-box;
}
.switch-label:before {
    content: attr(data-off);
    right: 11px;
    color: #FFFFFF;
    text-shadow: 0 1px rgba(255, 255, 255, 0.5);
}
.switch-label:after {
    content: attr(data-on);
    left: 11px;
    color: #FFFFFF;
    text-shadow: 0 1px rgba(0, 0, 0, 0.2);
    opacity: 0;
}
.switch-input:checked ~ .switch-label {
    background: #E1B42B;
    box-shadow: inset 0 1px 2px rgba(0, 0, 0, 0.15), inset 0 0 3px rgba(0, 0, 0, 0.2);
}
.switch-input:checked ~ .switch-label:before {
    opacity: 0;
}
.switch-input:checked ~ .switch-label:after {
    opacity: 1;
}
.switch-handle {
    position: absolute;
    top: 4px;
    left: 4px;
    width: 28px;
    height: 28px;
    background: linear-gradient(to bottom, #FFFFFF 40%, #f0f0f0);
    background-image: -webkit-linear-gradient(top, #FFFFFF 40%, #f0f0f0);
    border-radius: 100%;
    box-shadow: 1px 1px 5px rgba(0, 0, 0, 0.2);
}
.switch-handle:before {
    content: "";
    position: absolute;
    top: 50%;
    left: 50%;
    margin: -6px 0 0 -6px;
    width: 12px;
    height: 12px;
    background: linear-gradient(to bottom, #eeeeee, #FFFFFF);
    background-image: -webkit-linear-gradient(top, #eeeeee, #FFFFFF);
    border-radius: 6px;
    box-shadow: inset 0 1px rgba(0, 0, 0, 0.02);
}
.switch-input:checked ~ .switch-handle {
    left: 74px;
    box-shadow: -1px 1px 5px rgba(0, 0, 0, 0.2);
}

/* Transition
========================== */
.switch-label, .switch-handle {
    transition: All 0.3s ease;
    -webkit-transition: All 0.3s ease;
    -moz-transition: All 0.3s ease;
    -o-transition: All 0.3s ease;
}
.switch-left-right .switch-label {
    overflow: hidden;
}
.switch-left-right .switch-label:before, .switch-left-right .switch-label:after {
    width: 20px;
    height: 20px;
    top: 4px;
    left: 0;
    right: 0;
    bottom: 0;
    padding: 11px 0 0 0;
    text-indent: -45px;
    border-radius: 20px;
    box-shadow: inset 0 1px 4px rgba(0, 0, 0, 0.2), inset 0 0 3px rgba(0, 0, 0, 0.1);
}
.switch-left-right .switch-label:before {
    background: #FF7F50;
    text-align: left;
    padding-left: 80px;
}
.switch-left-right .switch-label:after {
    text-align: left;
    text-indent: 9px;
    background: #FF7F50;
    left: -100px;
    opacity: 1;
    width: 100%;
}
.switch-left-right .switch-input:checked ~ .switch-label:before {
    opacity: 1;
    left: 90px;
}
.switch-left-right .switch-input:checked ~ .switch-label:after {
    left: 0;
}
.switch-left-right .switch-input:checked ~ .switch-label {
    background: inherit;
}

I'm trying to set it up so that when the switch is on Diagnostic, it will unhide a group of form fields and if it's on progress it will hide the same form fields. I've tried event listeners and onclick listeners and couldn't seem to get anything working. I just need to get it as far as "if it's in one position, do this" and "if it's in the other position, do that" This doesn't seem like it would be a challenge, but its proving to be one!