Having a high workload and being pushed to your limits is better than being stuck somewhere with little or nothing to do. I you are always challenged and it becomes the norm for you it means you will always work hard and to a high standard. If you don't have much to do it makes it so much harder later when suddenly a lot is expected of you.
Even if you are tired now, the results of the work will stay with you and help you build your reputation with your colleagues and in your industry which benefits you and your career in the long run. And seeing a successful project come to completion is very satisfying in itself :)
I've had a couple projects like that, one in particular where I led a development team to create an in-house software solution for events management that expanded to cover the whole organisation involving many different stakeholders. It was stressful because so many people were counting on me getting it right and meeting their expectations. It was stressful but so satisfying when it was done. Another was organising moving our organisation from our old office building to a new one that was being built for us. I saw it through from the start of the construction of the new building to move in day. THAT was stressful as you had so many personal demands and requirements from various staff, but once it was done it gave me a real send of pride.
Good luck with your project, I'm sure it will be a huge success :) Tell us all about it when its done!