A very very simple Health controller with constant health drain

HealthController.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI; // Import the UI module.

public class HealthController : MonoBehaviour
{
    public Slider HealthBar;
    public Text HealthBarTextValue;

    /// ### PROPERTY ###
    private float _health = 100; // The real value
    public float Health // The accessible value
    {
        get => _health; // When we get the health, give them the real value.
        set
        {
            // Update the real value.
            _health = value;

            // Update the GUI / HUD.
            HealthBar.value = _health;
            HealthBarTextValue.text = ((int) _health).ToString();
        }
    }

    void Update()
    {
        Health -= Time.deltaTime * 10; // Drain our health at 10 point per second.
    }
}