LinqPad Script to avoid the sleep mode on running DISM command.

SetThreadExecutionStateWindow.linq

<Query Kind="Program">
  <Reference>&lt;RuntimeDirectory&gt;\WPF\PresentationCore.dll</Reference>
  <Reference>&lt;RuntimeDirectory&gt;\WPF\PresentationFramework.dll</Reference>
  <Reference>&lt;RuntimeDirectory&gt;\WPF\PresentationUI.dll</Reference>
  <Reference>&lt;RuntimeDirectory&gt;\System.Threading.Tasks.dll</Reference>
  <Reference>&lt;RuntimeDirectory&gt;\System.Xaml.dll</Reference>
  <Reference>&lt;RuntimeDirectory&gt;\WPF\WindowsBase.dll</Reference>
  <Namespace>System.ComponentModel</Namespace>
  <Namespace>System.Diagnostics</Namespace>
  <Namespace>System.Runtime.InteropServices</Namespace>
  <Namespace>System.Threading.Tasks</Namespace>
  <Namespace>System.Windows</Namespace>
  <Namespace>System.Windows.Controls</Namespace>
</Query>

[Flags]
enum EXECUTION_STATE : uint
{
	ES_SYSTEM_REQUIRED = 0x00000001,
	ES_DISPLAY_REQUIRED = 0x00000002,
	ES_AWAYMODE_REQUIRED = 0x00000040,
	ES_CONTINUOUS = 0x80000000,
	ES_DONE = ES_CONTINUOUS,
	ES_KEEP_ALIVE = ES_SYSTEM_REQUIRED | ES_DISPLAY_REQUIRED | ES_AWAYMODE_REQUIRED | ES_CONTINUOUS,
}

[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
static extern uint SetThreadExecutionState(EXECUTION_STATE esFlags);

public void Main()
{
	new MonitoringWindow().Show();
}

public class MonitoringWindow : Window
{
	Button startButton = new Button { Content = "Start", Margin = new Thickness(5) };
	Button cancelButton = new Button { Content = "Cancel", Margin = new Thickness(5), IsEnabled = false };
	TextBlock resultText = new TextBlock { Margin = new Thickness(5) };
	StackPanel stackPanel = new StackPanel();
	CancellationTokenSource cancelSource = null;

	public MonitoringWindow()
	{
		InitializeComponent();
	}

	async void startButton_Click(object sender, EventArgs args)
	{
		startButton.IsEnabled = false;
		cancelButton.IsEnabled = true;
		SetThreadExecutionState(EXECUTION_STATE.ES_DONE);
		resultText.Text = "Waiting...";
		cancelSource = new CancellationTokenSource();
		var token = cancelSource.Token;

		try
		{
			while (true)
			{
				bool foundDism = false;
				var processes = Process.GetProcesses();
				foreach (var process in processes)
				{
					if (process.ProcessName.ToLower() == "dism")
					{
						foundDism = true;
						SetThreadExecutionState(EXECUTION_STATE.ES_KEEP_ALIVE);
						resultText.Text = "Dism found...\n";
						resultText.Text += $"Id\t\t: {process.Id}\n";
						resultText.Text += $"StartTime\t: {process.StartTime}\n";
						resultText.Text += $"Now\t\t: {DateTime.Now}\n";
						break;
					}
					token.ThrowIfCancellationRequested();
				}
				if (!foundDism)
				{
					resultText.Text = "Finished.";
					break;
				}
				await Task.Delay(5000, token);
			}
		}
		catch (OperationCanceledException)
		{
			resultText.Text = "Monintoring Canceled";
		}
		catch (Exception ex)
		{
			resultText.Text = "Error: " + ex.Message;
		}
		finally
		{
			startButton.IsEnabled = true;
			cancelButton.IsEnabled = false;
			SetThreadExecutionState(EXECUTION_STATE.ES_DONE);
			cancelSource = null;
		}
	}

	void InitializeComponent()
	{
		Title = "Dism keeper";
		startButton.Click += startButton_Click;
		cancelButton.Click += (sender, e) => cancelSource.Cancel();
		Width = Height = 400;
		Padding = new Thickness(15);
		stackPanel.Children.Add(startButton);
		stackPanel.Children.Add(cancelButton);
		stackPanel.Children.Add(resultText);
		Content = stackPanel;
	}
}