How can we overcome discouragement due to constant mental lethargy?

From: Raja Rama Dasa

Eventhough we know that services such as book distribution, preaching etc. are very much required to uplift us and others as well, sometimes feel morose, lethargy in actually taking the body and mind out to service. I feel this is definitely the effect of modes of nature on me. How should I get out of this? I want to do more service but many times mind doesn’t favour. Due to this I lose enthusiasm altogether. How to overcome? Please help..