In short

Japanese turns “unbearably” into a suffix. て-form + たまらない (tamaranai) says a feeling is more than you can stand - 暑くてたまらない, unbearably hot; ない-stem + ずにはいられない (-zu ni wa irarenai) says you cannot stop yourself doing something - 笑わずにはいられない, I can’t help laughing. A second, much stiffer family (〜極まりない, 〜の至り, 〜を禁じ得ない, 〜てやまない) says “to the utmost degree” and belongs to speeches and print - learn to read it, not to chat with it.

The rule

Step 1 - 〜てたまらない: the feeling exceeds you. Attach たまらない to the て-form of a predicate that describes a feeling or a bodily sensation. The connector follows the ordinary te-form rules of lesson 13, so the shape depends on the word class:

• い-adjective, 〜くて - 暑い -> 暑くてたまらない (atsukute tamaranai) unbearably hot
• な-adjective / noun, 〜で - 心配 -> 心配でたまらない (shinpai de tamaranai) worried sick
• 〜たい, 〜くて - 会いたい -> 会いたくてたまらない (aitakute tamaranai) dying to see someone
• Verb, 〜て - only verbs of inner feeling: 気になってたまらない (ki ni natte tamaranai) it keeps nagging at me

Politely it is たまりません. The kanji 堪る exists but the word is normally written in kana.

Step 2 - The first-person restriction. たまらない and its relatives report a feeling from the inside, so the subject is normally the speaker (or, in a question, the listener). You cannot look at someone else and assert their inner state directly: ×彼は寂しくてたまりません。For a third person you must hedge with ようだ／らしい (lesson 49) or switch to the outward-sign suffix 〜がる: 彼は寂しくてたまらないようです / 彼は寂しがっています. This restriction applies to every pattern in Step 1 and Step 3.

Step 3 - The two colloquial twins, and the written one. Three auxiliaries share the te-form slot but not the register:

• 〜てしかたがない (-te shikata ga nai) - literally “there is no way to deal with it”. Neutral, usable in speech and in writing.
• 〜てしょうがない (-te shō ga nai) - the everyday spoken contraction of 〜てしようがない; the most frequent of the three in conversation, and the most casual. 眠くてしょうがありません (nemukute shō ga arimasen) I’m desperately sleepy.
• 〜てならない (-te naranai) - written, and narrower. Its home ground is feelings and thoughts that arise by themselves: 気になってならない, 思えてならない (omoete naranai) I can’t help thinking, 残念でならない (zannen de naranai) I find it deeply regrettable. A plain bodily sensation is not ungrammatical with it (この毛皮は暑くてならない, this fur is unbearably warm) but is much less usual - for those, reach for たまらない or しょうがない.

So: たまらない = anything you feel, spoken or written. しょうがない／しかたがない = the same, spoken. ならない = spontaneous emotion and thought, in print.

Step 4 - 〜ずにはいられない: you cannot stop yourself. Build it in two moves. Step 4a - make the ない-form and drop ない (the same base as 〜ずに in lesson 54). Step 4b - add ずにはいられない. The は is the contrastive topic particle, romanized wa; いられない is the potential negative of いる, so the literal sense is “cannot be without doing”.

• V-ない-stem + ずにはいられない - 笑わずにはいられません (warawazu ni wa iraremasen) I can’t help laughing.
• The one irregular is する -> せ: ×しずには -> ○ せずにはいられない (sezu ni wa irarenai). 来る, though an irregular verb, follows the rule here: 来ない -> 来ずに (kozu ni).
• 〜ないではいられない (-nai de wa irarenai) is the same meaning in a more conversational shape: 笑わないではいられません.

Compare 〜ざるを得ない (lesson 63). Both translate as “cannot but”, and the difference is where the pressure comes from. 〜ざるを得ない = external compulsion - rules, orders, facts leave you no option (認めざるを得ません, I have no choice but to admit it). 〜ずにはいられない = internal urge - your own emotion pushes you (認めずにはいられません, I can’t help admitting it).

Step 5 - Extremity, as fixed formal expressions. These are set phrases, not productive grammar. Attach them exactly as the table below shows and keep to the stock collocations.

• な-adjective stem + 極まりない／極まる (kiwamarinai / kiwamaru) - 失礼極まりない (shitsurei kiwamarinai) unspeakably rude, 危険極まる (kiken kiwamaru) extremely dangerous. The two are synonymous despite the ない: this ない is not a negation you may flip. Read 極まりない as “there is no limit to how X it is”. Mostly negative qualities.
• Noun + の極み (no kiwami) - 贅沢の極み (zeitaku no kiwami) the height of luxury, 痛恨の極み (tsūkon no kiwami) a matter of the deepest regret.
• Noun + の至り (no itari) - 光栄の至り (kōei no itari) the greatest of honours, 恐縮の至り (kyōshuku no itari) I am mortified, and the frozen idiom 若気の至り (wakage no itari) the folly of youth. Speeches, awards, formal apologies.
• い-adjective (or な-adjective + な) + 限りだ (kagiri da) - only emotion adjectives, only about yourself: うれしい限りです (ureshii kagiri desu) I couldn’t be happier, 羨ましい限りです.
• Noun + を禁じ得ない (o kinjienai) - “cannot suppress”, used with nouns of emotion: 同情を禁じ得ません (dōjō o kinjiemasen) I cannot suppress my sympathy, 驚きを禁じ得ません. Journalism and formal statements.
• V-て + やまない (yamanai, from 止む “cease”) - “unceasingly”, with a tiny verb set: 祈る, 願う, 愛する, 期待する, 尊敬する. ご活躍を祈ってやみません (inotte yamimasen) I sincerely wish you every success.

Forms & patterns

Attaching たまらない / しょうがない / ならない:

Which one to use:

Building ずにはいられない by verb class:

The extremity set (recognition first):

Examples

Common mistakes

• 暑いてたまりません。 (Atsuite tamarimasen.) -> 暑くてたまりません。 (Atsukute tamarimasen.) - たまらない takes a real te-form, and an い-adjective builds it with 〜くて. There is no ×〜いて.
• 心配てたまりません。 (Shinpai te tamarimasen.) -> 心配でたまりません。 (Shinpai de tamarimasen.) - な-adjectives and nouns join with で, exactly as in ordinary te-form linking.
• びっくりしずにはいられませんでした。 (Bikkuri shizu ni wa iraremasen deshita.) -> びっくりせずにはいられませんでした。 (Bikkuri sezu ni wa iraremasen deshita.) - before ず, する uses the base せ, never し. This single verb is the whole irregularity of the pattern: even 来る simply follows its 来ない.
• 彼は寂しくてたまりません。 (Kare wa sabishikute tamarimasen.) -> 彼は寂しくてたまらないようです。 (Kare wa sabishikute tamaranai yō desu.) - you cannot assert someone else’s inner state flatly. Hedge with ようだ (note the plain たまらない before ようです) or use 寂しがっています.
• 贅沢の極まりです。 (Zeitaku no kiwamari desu.) -> 贅沢の極みです。 (Zeitaku no kiwami desu.) - the noun after の is 極み; 極まりない is the separate adjectival form (贅沢極まりない). Do not blend the two.

Tips

• Two shelves, and only the lower one is for speaking. たまらない, しょうがない and ずにはいられない are things you can genuinely say. ならない, 極まりない, の極み, の至り, を禁じ得ない and てやまない are things you read - in editorials, award speeches, obituaries and formal apologies. Using 光栄の至りです over coffee is as odd as saying “I am most gratified” to a friend.
• 極まりない does not mean “not extreme”. The ない is welded on: 危険極まる and 危険極まりない are the same sentence. Store it as “there is no limit to how X this is” and the polarity stops bothering you.
• Ask “who is pushing?” to choose between ずにはいられない and ざるを得ない. If the pressure is your own emotion, it is ずにはいられない; if it is rules, evidence or other people, it is ざるを得ない (lesson 63). English “I can’t help but …” covers both and will not help you decide.
• Learn the の至り phrases whole. Only a handful are current - 光栄の至り, 恐縮の至り, 感激の至り, 若気の至り - and 若気の至り is a plain idiom for a youthful blunder, not a compliment. Memorise these; do not invent your own.