If you are still feeling this way, you might want to try contrast showers or some other means of alternating hot and cold. It’s probably only going to be a short term fix in your case, since you have a viral issue, but you might find that it helps give you a short term boost immediately in concentration/intensity immediately following the therapy. Make sure the cold is very cold and being applied especially to temperature sensitive areas such as the plexus and neck. You want your heart rate to spike up and then come right back down once heat is applied. And, particularly if you are using a whole body method of temperature contrast, make sure to check muscle tonus before any high intensity work. Just a suggestion.