A simple camera shake that just shakes the camera from its current rotation and resets it back to its original location. Forked from http://wiki.unity3d.com/index.php/Camera_Shake

SimpleCameraShake.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SimpleCameraShake : MonoBehaviour
{
    public static SimpleCameraShake Instance;

    float shakeAmount;
    float shakeDuration;
    float shakePercentage;
    float startAmount;
    float startDuration;

    bool isRunning = false;

    bool smooth;
    float smoothAmount = 5f;

    private void Awake()
    {
        if (Instance == null)
        {
            Instance = this;
        }
        else if (Instance != this)
        {
            Destroy(this);
        }
    }

    public void ShakeCamera(float amount, float duration, bool _smooth = true, float _smoothAmount = 5f)
    {
        shakeAmount += amount;
        startAmount = shakeAmount;
        shakeDuration += duration;
        startDuration = shakeDuration;

        smooth = _smooth;
        smoothAmount = _smoothAmount;

        if (!isRunning) StartCoroutine(Shake());
    }


    IEnumerator Shake()
    {
        isRunning = true;
        Quaternion startingRotation = transform.localRotation;

        while (shakeDuration > 0.01f)
        {
            Vector3 rotationAmount = Random.insideUnitSphere * shakeAmount;
            rotationAmount.z = 0;

            shakePercentage = shakeDuration / startDuration;

            shakeAmount = startAmount * shakePercentage;
            shakeDuration = Mathf.Lerp(shakeDuration, 0, Time.deltaTime);

            Quaternion roateTo = Quaternion.Euler(startingRotation.eulerAngles + rotationAmount);

            if (smooth)
                transform.localRotation = Quaternion.Lerp(transform.localRotation, roateTo, Time.deltaTime * smoothAmount);
            else
                transform.localRotation = roateTo;

            yield return null;
        }
        transform.localRotation = startingRotation;
        isRunning = false;
    }
}