I wish I had a lot of energy and discipline and I could study, read, work, for hours without interruptions.
That’s not a matter of energy or discipline - it’s called life. We all live in societies with other people, who interrupt us whether we like it or not. Unless you become a total hermit who doesn’t even interact with other hermits, our time is NEVER so entirely our own that we can control interruptions to the extent that you seem to want to.
Even for those whose time IS entirely their own, it’s human nature - we aren’t machines, we need rest, we need breaks, we need a variety of tasks and activities in our days, and we don’t function properly without them. We’re built that way.
I am always active in a way, but I always go to sleep with feelings of guilt that I haven’t been active enough, done enough things, spent too much time on Facebook or doing something not useful.
How active is active ‘enough’? Where in scriptures, for example, does it say ‘thou shalt work 8/10/12 hours a day’? And what exactly makes you think that being ‘always active in a way’ does not qualify as ‘active enough’?
Please don’t get sucked into this idea that spending some time each day on non-productive activity is anything other than healthy and normal. Your thinking is tied in to the idea that ‘you are what you produce’, which Our Lord has surely shown us is wrong.
It’s in fact another form of distraction - only instead of distracting yourself with facebook or whatnot, you distract yourself with other tasks that you falsely imagine to be more ‘important’ or more ‘worthy’.
Remember what Our Lord said about worrying about what we’re going to eat, how we’re going to clothe ourselves and the like things that we tend to think of as being important. Apart from prayer and charitable work, most EVERYTHING we do is of very secondary importance in the grand scheme of things, whatever value we may place on it.
Remember too, only robots can work at maximum capacity for hours on end, and even they break down fairly quickly when worked in such a way. Humans, being much more fragile than machinery, break down very quickly indeed when they are overworked.
There’s even an episode in the Gospels where Jesus sees how overworked and overwhelmed the Apostles are and takes them off to a quiet place to be by themselves and rest. Meditate on that for a while.
It’s the battle I’m fighting all my life. Do you have any ideas, practical or spiritual, advice, how to beat this? How to be as active as I want to be? How not to waste time? Nowadays media/Internet tempt us with useless “activities” all the time.
See above - unless you’re spending many hours a day every day in front of the tv screen or on the internet or something, then you’re not close to the sin of sloth.