Idle Randomiser

Despite how much I agree with dorpeleg, I understand your position. I'm a programmer, not an animation expert, which gives me a lot of trouble in development. Here's a basic example of how you can do what you want to do, with thorough notes on what I'm doing.

 using UnityEngine;
 using System.Collections;
 using System;
 
 public class IdleStance : MonoBehavior
 {
     protected int totalAnims = 10; 
     // Set this to your total number of animations
     
     public Animation firstIdle;
     // Define your original animation
     
     public Animation[] idleAnims = new Animation[totalAnims]; 
     // Create an array of your animations, you can define them in the inspector
     
     public GameObject thePlayer;
     // Define your player in the inspector
     
     protected float walkTime;
     // This will be for a time checker
     
     float waitTime = 5.0f;
     
     protected bool isMoving = false, hasPlayed = false;
     // Create false bools for if you're moving and if the first animation has played
     
     public void Update()
     {
         if(thePlayer.rigidbody.velocity.magnitude > 0)
         {
             // If you're moving, set isMoving to true
             isMoving = true;
             // And set walkTime to the current time
             walkTime = Time.time;
         }else{
             // Else set it to || leave it as false
             isMoving = false;
         }
         
         if(!isMoving)
         {
             // If you're not moving,
             if(walkTime - Time.time > waitTime)
             {
                 // And x amount of seconds have passed
                 if(!hasPlayed)
                 {
                     // If this is you first stopping, play the original animation
                     firstIdle.Play();
                     hasPlayed = true;
                 }
                 if(!firstIdle.isPlaying())
                 {
                     // If it's you continuing to wait, get a random animation
                     int randomAnim = random.Next(0, idleAnims.Length);
                     // And play it.
                     Animation toPlay = idleAnims[randomAnim];
                     toPlay.Play();
                 }
             }else{
                 // If you start moving, set your hasPlayed bool to false
                 hasPlayed = false;
             }
         }
     }
 }