It is essential that you take the time to build appropriate rest periods into your schedule, planned in the same way that you plan your workouts.
Not only do you need to be sure to get enough sleep (athletes need at least 8 hours per night to give the body time to recover day to day), you also need to consider the following:
- Schedule one or two days off per week
- Alternate hard and easy days (or for triathletes, two hard, one easy)
- Plan a monthly training cycle of three hard weeks followed by one easy week (easy meaning 50% of training volume)
- Cycling your training volume through the year (periodization) so that you have periods of higher and lower volume
- Planning one month per year of very low, recovery training (typically after your season ends)
The bottom line is that to perform at your maximum when you really need to (e.g. in competition) you need to get plenty of sleep and schedule days off - you'll not only feel better, you'll achieve your workout goals sooner, and perform better in competition.