SuttaCentral
There is one sutta where the Buddha explains how during meditation he would initially get too excited and elated and how this was equally as bad as being too dull and serious while meditating.
Feels like I haven’t read it for ages and I can’t find which specific sutta it is when searching, all help finding the sutta in question is greatly appreciated!
It seems this is MN128, the Upakkilesasutta, where various sorts of corruptions are discussed.
@Dhabba
You didn’t mark your inquiry as “solved”, so maybe you are still looking? What sprang to mind is the famous harp’s string-tuning simile. I have heard Dhamma teachers applying it to meditation instructions.
It’s in AN 6.55
Hi @thistle! 
Oh sorry, I didn’t know I could mark it as ”solved”.
I just gave a heart to @sabbamitta yesterday and then immediately went on a walk with my dog while listening to MN 128!
The thing is when I was back home from that walk I not only wanted to write thanks but also mention a thing that happened while walking my dog that I found funny but thought maybe others here reading that post would find it very inappropriate, so I decided not to write anything at all. 
But to give you an idea, I was listening to the audiobook of MN 128 with headphones.
Others passing me by very close to me can clearly hear the speech from the suttas from my headphones… 
A family passed me by just while I was standing with my dog and they obviously heard the things said in the next sutta MN 129 totally out of context, only snippets, they must have thought I’m a very deranged person! 
Worst timing ever…
I’ve had similar but way worse moments with audiobook suttas, like while standing in line in the grocery store where all of a sudden what is actually being said in the suttas are things that no sane person would ever listen to! 
Totally out of context.
I’ve know which suttas to ”avoid” so to speak But I haven’t heard MN 128 in a long time so I was not prepared for the things being said in MN 129 at all. 
No worries! I just mentioned it because I think it’s a very useful feature 
I can absolutely relate to that! I’m fighting the urge quite often, i.e. to post something which I think is funny but then refrain from doing so because it could be regarded as inappropiate.
Yes, I can imagine that some snippets out of context would sound weird if one is not familiar with the context. Or - perhaps- it might be the ice-breaker for an earnest conversation if circumstances are favourable. 
SN46.53 is also relevant.
I think answering the initial question would depend on what “meditation” means, and what exactly one does when, “...kālo tasmiṁ samaye --sambojjhaṅgassa bhāvanāya” occurs.
I also wonder in Majjhima 128, where the phrase, “Idha mayaṁ, bhante, appamattā ātāpino pahitattā viharantā..” is translated as " while meditating," what that might entail…what are the instructions?
(it is literally, “as we dwell here…”)
Mendicants, a mendicant committed to the higher mind should focus on three bases from time to time: the basis of immersion, the basis of exertion, and the basis of equanimity.
If a mendicant dedicated to the higher mind focuses solely on the basis of immersion, it’s likely their mind will incline to laziness.
If they focus solely on the basis of exertion, it’s likely their mind will incline to restlessness.
If they focus solely on the basis of equanimity, it’s likely their mind won’t properly become immersed in samādhi for the ending of defilements.
But when a mendicant dedicated to the higher mind focuses from time to time on the basis of immersion, the basis of exertion, and the basis of equanimity, their mind becomes pliable, workable, and radiant, not brittle, and has become rightly immersed in samādhi for the ending of defilements.
It’s like when a goldsmith or a goldsmith’s apprentice prepares a forge, fires the crucible, picks up some native gold with tongs and puts it in the crucible. From time to time they fan it, from time to time they sprinkle water on it, and from time to time they just watch over it. If they solely fanned it, the native gold would likely be scorched. If they solely sprinkled water on it, the native gold would likely cool down. If they solely watched over it, the native gold would likely not be properly processed. But when that goldsmith fans it from time to time, sprinkles water on it from time to time, and watches over it from time to time, that native gold becomes pliable, workable, and radiant, not brittle, and is ready to be worked. Then the goldsmith can successfully create any kind of ornament they want, whether a bracelet, earrings, a necklace, or a golden garland.
In the same way, a mendicant committed to the higher mind should focus on three bases from time to time: the basis of immersion, the basis of exertion, and the basis of equanimity. …
When a mendicant dedicated to the higher mind focuses from time to time on the basis of immersion, the basis of exertion, and the basis of equanimity, their mind becomes pliable, workable, and radiant, not brittle, and has become rightly immersed in samādhi for the ending of defilements. They extend the mind to realize by insight each and every thing that can be realized by insight; and they are capable of realizing those things, since each and every one is within range.
If they wish: ‘May I wield the many kinds of psychic power’ …
‘With clairaudience that is purified and superhuman, may I hear both kinds of sounds, human and divine, whether near or far.’ … ‘May I recollect many kinds of past lives.’ … ‘With clairvoyance that is purified and superhuman, may I see sentient beings passing away and being reborn.’ … ‘May I realize the undefiled freedom of heart and freedom by wisdom in this very life, and live having realized it with my own insight due to the ending of defilements.’ They are capable of realizing these things, since each and every one is within range.”
AN 3.102
Also see SN 47.8 and SN 47.10 for more suttas on the theme of “balanced” practice.