Ajax autocomplete using Post leads to "The connection was reset" error and "net::ERR_EMPTY_RESPONSE" console error

Question

Hello and thank you for taking the time to read my question.

My website is hosted on Godaddy and I have the "Deluxe Linux Hosting package".

My webpage helps users to find markets using a simple form, which uses JQuery, Ajax, PHP and MySQL to show suggestions relevant to their search term.

I am using an autocomplete function in a the search field so that when users type in their search term, the relevant suggestions appear below the input field in a div with the id 'list_area'.

The suggestions are being populated by JQuery and a PHP script, which is being fed the search terms via the AJAX "Post" method (now the AJAX method as I wanted to log the errors to the console).

Here is where the js script is called in the HTML page:

<input autocomplete="off" type="text" 
class="form-control input-lg" name="market_search" 
id="market_search" placeholder="Enter a market name" 
onkeyup="autoComplete();">

There is also a preventDefault function on the same page to prevent the form from being submitted without a search term:

    <script>                    
        $( "#search_form" ).submit(function(e) {                            
            if( $('#market_search').val() =='' ){
                e.preventDefault();
            }                       
        });                     
    </script>   

Here is Autocomplete.js

function autoComplete()
{   
    var list_area   = $('#list_area');
    var min_length  = 1; 
    var search_term = $('#market_search').val();

    if (search_term.length >= min_length) { 

        $.ajax({
            type: 'POST',
            url: 'assets/scripts/search_markets.php',
            data: {
            search_term: search_term
            },
            success: function(data){

                list_area.hide().html(data).fadeIn('fast');
                console.log(status);                
            },
            error: function(xhr, textStatus, error){
                alert("Unable to retrieve data. Please try again.");
                console.log(xhr.statusText);
                console.log(textStatus);
                console.log(error);
            }
        });

    }else{
        list_area.hide();
    }
}


function set_item(item) {

    // change input value
    $('#market_search').val(item);

    // hide proposition list
    $('#list_area').hide();
}

Here is search_markets.php

<?php
include("connect_to_mysql.php");

$output = '';
$search_term = mysql_real_escape_string($_POST['search_term']);

$sql = mysql_query("
                    SELECT name FROM markets 
                    WHERE name LIKE '%$search_term%' 
                    ORDER BY name LIMIT 0,10
                   ");

$num_rows = mysql_num_rows($sql);

if($num_rows > 0){

    $output .= '<ul>';
    while($row = mysql_fetch_array($sql)){

        $market_name = $row['name'];
        $market_name = preg_replace('/\s{2,}/u', ' ', $market_name); // replaces large spaces with single space between words

        $output .='<li onclick="set_item(\''.str_replace("'", "\'", $market_name).'\');">'.$market_name.'</li>';                
    }
    $output .= '</ul>';
}
echo($output);
mysql_close($mysql_conn);
?>

The code behaves as you would expect and returns a list of suggestions in the #list_area div.

However, if you use the search field too much within the space of around 30 seconds - i.e. you type in a letter, delete the letter, type in a letter, and do so a few times etc etc - the suggestions stop appearing and the site becomes temporarily unavailable should you try to navigate to the homepage.

This error shows up: "The connection was reset"

And in Chrome I get the error: "net::ERR_EMPTY_RESPONSE"

In Firefox, I don't get that error code, it just highlights the attempted connection to search_markets.php in red, and no more details are given.

I put the question here as I am a bit of a novice, and unsure how to even begin searching for a solution; google searches on the errors in relation to my situation have not been much help, and I am unsure if it is a server issue, a browser issue, or a code issue.

Much thanks in advance for any help you can offer.