Ο συναγερμός χτύπησε απότομα και πετάχτηκα από το κρεβάτι.

Not usually. Συναγερμός most often means alarm, alert, siren, security alarm. If you specifically mean an alarm clock, Greek more commonly uses ξυπνητήρι.

So in everyday Greek, if you mean The alarm clock rang, you will often hear:

Το ξυπνητήρι χτύπησε.

In your sentence, συναγερμός sounds more like a general alarm signal, or a more dramatic kind of alarm.

Because χτυπάω / χτυπώ does not only mean hit. It is also commonly used for things that ring, sound, or go off, such as:

• το τηλέφωνο χτυπάει = the phone is ringing
• το κουδούνι χτύπησε = the bell rang
• ο συναγερμός χτύπησε = the alarm went off

So here χτύπησε is a very natural verb.

Απότομα means abruptly, suddenly, sharply. In this sentence it adds the idea that the alarm sounded in a sudden, jolting way.

So it is not just that the alarm rang, but that it rang abruptly, which helps explain the strong reaction in the second half of the sentence.

A nearby word is ξαφνικά (suddenly), but απότομα often gives a stronger sense of suddenness or abruptness.

Both are in the aorist, which is the main Greek past tense for a single completed event.

Here it is used to tell a short sequence of events:

• χτύπησε = it rang / went off
• πετάχτηκα = I jumped up / sprang out

This is very typical narrative Greek: one event happened, then another happened.

That is a very common learner question. Πετάχτηκα is the aorist form used for πετάγομαι, and although the form looks like a passive-type form, the meaning here is not passive.

In this sentence, πετάχτηκα means:

• I sprang up
• I jumped up
• I jumped out

It does not mean I was thrown here.

Greek has a number of verbs that use middle/passive-looking forms but have active or intransitive meanings in actual use.

Because Greek often leaves out subject pronouns when they are already clear from the verb ending. This is called a pro-drop language.

The ending in πετάχτηκα already tells you the subject is I.

So:

• πετάχτηκα = I jumped up

You could add εγώ if you want emphasis:

και εγώ πετάχτηκα από το κρεβάτι

But without emphasis, Greek normally omits it.

Yes. With verbs of movement, από often means from or away from, and in this expression it naturally gives the sense of out of bed or up from bed.

So:

πετάχτηκα από το κρεβάτι
means something like
I jumped out of bed / I sprang up from bed

A more literal phrase with έξω από would sound less natural here. Greek often uses just από in this kind of expression.

Literally it is just and, but in storytelling it often also carries the idea of sequence.

So in this sentence:

Ο συναγερμός χτύπησε απότομα και πετάχτηκα από το κρεβάτι.

the meaning is naturally understood as:

• The alarm went off abruptly and I jumped out of bed
• or even ...and then I jumped out of bed

Greek does not need a separate word for then here.

No, Greek word order is fairly flexible. The order here is natural and neutral for narration:

1. Ο συναγερμός χτύπησε απότομα
2. και πετάχτηκα από το κρεβάτι

This presents the cause first and the reaction second.

You can change the order for emphasis, but the tone changes too. For example:

Πετάχτηκα από το κρεβάτι όταν χτύπησε απότομα ο συναγερμός.

That still means roughly the same thing, but it focuses first on my reaction rather than on the alarm.