It's easy to forget, and with the increased sweating on a stationary bike in a warm room, it's easy to get dehydrated. And the general sense of unease that comes along with dehydration increases the fatigue and tedium of the session. Remember that having a plan helps fight the boredom, and is a key to making this a positive part of your training program. There are many plans available, but most have common themes. And another study of trained cyclists found that a poorer workout when they cranked up the decibels.
First thing is to set the rollers correctly.
Put the bike on the rollers and set the height of the front wheel the same as the rear one with adjusters or blocks of wood. If this is not done you will be riding up hill and the ballance will be wrong causing untold damage to the perineum etc. The next thing to do is to set the length the same as your bike. A plumb bob from the front axle of your bike should pass as close as possible to the centre of the front roller. After this check the level again.