How To Make Healthbar Value Slowly Decrease?

How do I make a healthbar value slowly decrease?

What I have:
public Slider Healthbar;

	void OnTriggerEnter(Collider enemy)
		Healthbar.value -= Random.Range(2, 5); // I need help here!

		if (Healthbar.value <= 0) {
			anim.Play ("Dead");

You could do something like…

Healthbar.value -= Random.Range(2,5) * Time.DeltaTime;

I’m not 100% sure if that line will work for what you want, but I have a feeling you need to incorporate the unity timescale into your code to reach the desired effect.