why did my imessages get turned off in the middle of the night and i lost some conversations?

There are two possibilities...

1. If you have pre-paid SIM and the SMS Plan has expired or the SIM validity has expired.
2. If your carrier disables the international SMS plan on your SIM, iMessage will automatically deactivate. This is because iMessage relies on SMS for activation in some situations, even if you don't intend to send international messages.

Read the following two points in conjunction during iMessage Activation (Applied in some countries)

1. If your iPhone is used with a carrier not found in the wireless carrier articles, make sure you can send and receive international SMS. (One international SMS*** Only)
2. If you can't turn on or sign in to iMessage or FaceTime - Apple ...

Here's why it gets de-activated automatically:

1. Activation Verification: When you first activate iMessage, your carrier needs to verify your phone number. This is typically done by sending an SMS to Apple's servers. If your international SMS plan is disabled, this verification cannot be completed, and iMessage won't activate.
2. Fallback Mechanism: Even after activation, iMessage might use SMS as a fallback if it can't deliver messages over data (iMessage or MMS). This can happen in areas with poor data connectivity or if the recipient's device doesn't support iMessage. Without an international SMS plan, these fallback messages cannot be sent, leading to potential message delivery failures and potentially triggering iMessage deactivation.

Therefore, it's crucial to be aware of your carrier's international SMS plan policies and potential impact on iMessage activation and functionality. If you frequently travel internationally or need iMessage to function reliably, consider enabling an international SMS plan even if you don't plan on sending international messages.

Here are some additional points to keep in mind:

• Some carriers might offer temporary international SMS plans or options to activate iMessage without them. Check with your carrier for details.
• You can always manually re-activate iMessage in your settings after your carrier enables your international SMS plan again.
• Regular backups of your device (including messages) can help you recover them if they are accidentally deleted or lost due to iMessage deactivation.

To activate iMessage and FaceTime using your Phone number

1. First, check to know whether you have an SMS plan enabled for at least One SMS*** with your carrier. Contact your Carrier (Cellular Service Provider) the agency that issued the SIM to you
2. If your iPhone is used with a carrier not found in the wireless carrier articles, make sure you can send and receive international SMS. (One international SMS*** Only)
3. If you can't turn on or sign in to iMessage or FaceTime - Apple ...

*** You may not have an SMS plan (Domestic & International) enabled by your carrier for the SIM/eSIM that you use on your device. Apple Inc does not provide SMS services.