what happens if you take antidepressants for no reason?!

That depends on what type of antidepressant you are talking about.

Tricyclics, such as Nortriptyline and Amitriptyline, can cause cardiac arrest when used improperly.

SSRIs (like Zoloft and Celexa) are relatively safer than tricyclics when used as prescribed, but they still have lots of the same negative side effects, such as low libido, weight gain, nausea, difficult urination, etc.

There are other classes of antidepressants, but they generally have the same side effects profile as the SSRIs.

There's really not a point in abusing antidepressants, because they don't give you a high like other drugs. Antidepressants work by increasing the amount of endogenous chemicals in your brain (serotonin, norepinephrine, dopamine). However, they do not stimulate the central nervous system and therefore do not produce a "high." Long term use may cause the body to under-produce said chemicals, causing a period of depression when the drugs are withdrawn; this is why it's important to wean patients off of antidepressants, rather than having them stop "cold turkey."

You would get all of the side effects without any of the benefits, really it's a loose loose situation.
Side effects would depend on the exact drug that your abusing?
General side effects are:

* Dry mouth
* Urinary retention
* Blurred vision
* Constipation
* Sedation (can interfere with driving or operating machinery)
* Sleep disruption
* Weight gain
* Headache
* Nausea
* Gastrointestinal disturbance/diarrhea
* Abdominal pain
* Inability to achieve an erection
* Inability to achieve an orgasm (men and women)
* Loss of libido
* Agitation
* Anxiety

And then there is the problem of when you decide not to take them any more you'll experience the withdrawal, which is not pleasant believe me.
It's your choice, your body, your life, but I wouldn't do it.
Good luck x